We present a theoretical study of the effects of collisions with water vapor molecules on the absorption, around 4 μm, in both the high frequency wing of the CO₂ ν₃ band and the collision-induced fundamental band of N₂. Calculations are made for the very first time, showing that predictions based on classical molecular dynamics simulations enable, without adjustment of any parameter, very satisfactory agreement with the few available experimental determinations. This opens the route for a future study in which accurate temperature-dependent (semi-empirical) models will be built and checked through comparisons between computed and measured atmospheric spectra. This is of interest since, as demonstrated by simulations, neglecting the humidity of air can lead to significant modifications of the atmospheric transmission (and thus also emission) between 2000 and 2800 cm⁻¹.

The high-resolution FTIR spectrum of the 2v₂ band (3250–3380 cm⁻¹) of D₂¹³CO was recorded at an unapodized resolution of 0.0063 cm⁻¹. A total of 747 rovibrational transitions have been assigned and fitted up to J″ = 32 and K_a″ = 10 using the Watson’s A-reduced Hamiltonian in the I^r representation. A set of accurate upper state (v₂= 2) rovibrational constants, three rotational and five quartic centrifugal distortion constants, were determined for the first time. The band center of the 2v₂ band was found to be 3326.765109 ± 0.000079 cm⁻¹. The rms deviation of the rovibrational fit was 0.00096 cm⁻¹.

The consistency of all data that have been published to date on the rovibrational line centers of the hydrogen chloride molecule HCl is analyzed. It was revealed that a number of corrections are needed because of systematic inaccuracies in the line center determination. A simultaneous fit of rovibrational transition frequencies was performed in the region from 7.4 to 18075 cm^–1. The isotopically independent spectroscopic parameters for calculating rovibrational energy levels in the ground electronic state are determined. The calculated line centers are compared with the HITRAN data. The obtained spectroscopic parameters are used to calculate the turning points (rmin and rmax) of RKR-potentials of HCl isotopologues. The use of experimental data, including the highest vibrational state with V_max = 8 that lies approximately at half the potential well depth allowed the pointwise potentials to be calculated up to Vmax = 20.

The FAIR guiding principles for research data stewardship (findability, accessibility, interoperability, and reusability) look set to become a cornerstone of research in the life sciences. A critical appraisal of these principles in light of ongoing discussions and developments about data sharing is in order. The FAIR principles point the way forward for facilitating data sharing more systematically — provided that a number of ethical, methodological, and organisational challenges are addressed as well.

The non-relativistic variational calculation of a complete set of ro-vibrational states in the H⁺₂ molecular ion supported by the ground 1sσ adiabatic potential is presented. It includes both bound states and resonances located above the n = 1 threshold. In the latter case we also evaluate a predissociation width of a state wherever it is significant. Relativistic and radiative corrections are discussed and effective adiabatic potentials of these corrections are included as supplementary files.

We present an accurate measurement of the weak quadrupole S(2) 2-0 line in self-perturbed D₂ and theoretical ab initio calculations of both collisional line-shape effects and energy of this rovibrational transition. The spectra were collected at the 247–984 Torr pressure range with a frequency-stabilized cavity ring-down spectrometer linked to an optical frequency comb (OFC) referenced to a primary time standard. Our line-shape modeling employed quantum calculations of molecular scattering (the pressure broadening and shift and their speed dependencies were calculated, while the complex frequency of optical velocity-changing collisions was fitted to experimental spectra). The velocity-changing collisions are handled with the hard-sphere collisional kernel. The experimental and theoretical pressure broadening and shift are consistent within 5% and 27%, respectively (the discrepancy for shift is 8% when referred not to the speed averaged value, which is close to zero, but to the range of variability of the speed-dependent shift). We use our high pressure measurement to determine the energy, ν₀, of the S(2) 2-0 transition. The ab initio line-shape calculations allowed us to mitigate the expected collisional systematics reaching the 410 kHz accuracy of ν₀. We report theoretical determination of ν₀ taking into account relativistic and QED corrections up to α⁵. Our estimation of the accuracy of the theoretical ν₀ is 1.3 MHz. We observe 3.4σ discrepancy between experimental and theoretical ν₀.

The technique of frequency-stabilized comb-calibrated cavity ring-down spectroscopy was used to observe the weak R(1) transition of the deuturated molecular hydrogen (HD) first overtone band in the near infrared. Like molecular hydrogen, HD is a benchmark system to test quantum electrodynamics, looking for new physics beyond the standard model. The spectral line shape was measured with an extremely high fidelity at relatively low gas pressures. The use of a very refined line-shape model allowed us to retrieve the unperturbed line-center frequency of the R(1) line with a global uncertainty of about 100 kHz (δν/ν=5×10−10). Our value may solve the ambiguity that recently emerged for this line from a pair of sub-Doppler experiments. We also determined other parameters of interest, such as the line strength, the transition dipole moment, and the pressure-broadening coefficien

The methane absorption spectrum is studied at 297 K and 80 K in the center of the Tetradecad between 5695 and 5850 cm⁻¹. The spectra are recorded by differential absorption spectroscopy (DAS) with a noise equivalent absorption of about α_min≈ 1.5 × 10⁻⁷ cm⁻¹. Two empirical line lists are constructed including about 4000 and 2300 lines at 297 K and 80 K, respectively. Lines due to ¹³CH₄ present in natural abundance were identified by comparison with a spectrum of pure ¹³CH₄ recorded in the same temperature conditions. About 1700 empirical values of the lower state energy level, E_emp, were derived from the ratios of the line intensities at 80 K and 296 K. They provide accurate temperature dependence for most of the absorption in the region (93% and 82% at 80 K and 296 K, respectively). The quality of the derived empirical values is illustrated by the clear propensity of the corresponding lower state rotational quantum number, J_emp, to be close to integer values. Using an effective Hamiltonian model derived from a previously published ab initio potential energy surface, about 2060 lines are rovibrationnally assigned, adding about 1660 new assignments to those provided in the HITRAN database for ¹²CH₄ in the region.

We report measurement results for line positions, intensities, half-width, and pressure-induced shift coefficients and line mixing coefficients for N2O broadened by air in the ν3 band. The high signal-to-noise ratio spectra have been recorded at high resolution using the McMath-Pierce Fourier transform spectrometer formerly located at the National Solar Observatory on Kitt Peak, Ariz., USA. The spectra were analyzed using a multispectrum nonlinear least-squares curve-fitting technique employing the speed-dependent Voigt profile with a Rosenkranz (weak) line mixing component. The speed dependence parameters were calculated as suggested in the study of Kochanov (J. Quant. Spectrosc. Radiat. Transf. 189, 18 (2017). doi:10.1016/j.jqsrt.2016.11.007). Several comparisons have been performed between the retrieved parameters and previously published results. For |m| ≤ 40, our results for line positions, broadening, and line mixing coefficients agree best with the results of Loos et al. (J. Quant. Spectrosc. Radiat. Transf. 151, 300 (2015). doi:10.1016/j.jqsrt.2014.10.008). Also, we compared the obtained line positions and intensities with the corresponding values in HITRAN2016 and GEISA-2015 databases. No significant or systematic differences were noticed. The precision of our line positions was estimated to be 3 × 10⁻⁵ cm⁻¹. The reported line positions, intensities, and air-broadening coefficients are accurate to better than 2%. The accuracy of air-pressure-induced line shifts and line mixing coefficients is better than 5%. The line mixing coefficients and air-broadening coefficients were also calculated using the exponential power gap scaling law, and these calculated values were found to be in good agreement with the experimental results.

Pure CO₂ spectra recorded at room temperature and different pressures (0.2–140 Torr) have been analyzed with the help of a fitting routine that takes into account asymmetries arising in the spectral lines due to pressure induced effects such as line mixing. The fitting procedure used in this study allows one to adjust the ro-vibrational constants for the band rather than fitting for individual line parameters. These constrained parameters greatly reduce the measurement uncertainties and allow us to observe the behavior of the weak lines corresponding to high J quantum numbers. We have also calculated line mixing parameters using approximations based on exponential nature of the energy difference between ground and upper vibrational states involved in the ro-vibrational band transitions. The calculated results show good agreement when compared with the experimentally determined parameters.

(J, K)-line broadening and shift coefficients with their temperature-dependence characteristics are computed for the perpendicular (ΔK = ±1) ν₆ band of the ¹²CH₃D-N₂ system. The computations are based on a semi-empirical approach which consists in the use of analytical Anderson-type expressions multiplied by a few-parameter correction factor to account for various deviations from Anderson's theory approximations. A mathematically convenient form of the correction factor is chosen on the basis of experimental rotational dependencies of line widths, and its parameters are fitted on some experimental line widths at 296 K. To get the unknown CH₃D polarizability in the excited vibrational state v₆ for line-shift calculations, a parametric vibration-state-dependent expression is suggested, with two parameters adjusted on some room-temperature experimental values of line shifts. Having been validated by comparison with available in the literature experimental values for various sub-branches of the band, this approach is used to generate massive data of line-shape parameters for extended ranges of rotational quantum numbers (J up to 70 and K up to 20) typically requested for spectroscopic databases. To obtain the temperature-dependence characteristics of line widths and line shifts, computations are done for various temperatures in the range 200–400 K recommended for HITRAN and least-squares fit procedures are applied. For the case of line widths strong sub-branch dependence with increasing K is observed in the R- and P-branches; for the line shifts such dependence is stated for the Q-branch.

Paper is dedicated to the new approach to distributed industrial systems (IS) sustainability/vulnerability assessment. This approach is based on the unitary multiset grammars (UMG) as a flexible and convenient tool designed specially for large systems analysis and optimization. UMG description of IS technological base as well as multiset representation of order completed by the IS, its resource base and impact on the IS are presented. Criterion for recognition of IS sustainability to the impact is formulated. UMG extension for natural disasters impacts (NDI) representation is introduced, and criterion for recognition of IS sustainability to the NDI is also presented. The solution of the reverse problem, concerning part of the order, which may be completed by the affected IS, is described. Implementation issues are considered.

This paper describes a Virtual Research Environment (VRE) based on a web GIS platform ‘­Climate+’, which provides an access to analytic instruments processing 19 collections of ­meteorological and climate data of several international organizations. This environment ­provides ­ystematization  sof spatial data and related climate information and allows a user getting ­analysis results using geoinformation technologies. The ontology approach to this ­ s ystematization is described, ­making it possible to match semantics of meteorological and climate parameters presented in different collections and used in solving various applied problems.

A low-resolution (0.5 cm⁻¹) Fourier transform infrared (FTIR) spectrum of formaldehyde-d₂ (D₂¹²CO) in the 2500–4500 cm⁻¹ region was recorded to study the combination bands in this region. The bands ν₂+ν₄, ν₂+ν₆, ν₂+ν₃, ν₁+ν₂, ν₂+ν₅, ν₂+ν_{5 ,} 3ν₃, 2ν₂ and 2ν₅ were identified and their band centers (with an uncertainty of ± 0.1 cm⁻¹) and band types were determined. Furthermore, the high-resolution FTIR spectrum of the 2ν₂ overtone band (3315–3440 cm⁻¹) of D₂¹²CO was recorded at an unapodized resolution of 0.0063 cm⁻¹ and its infrared lines were analyzed. A total of 970 rovibrational transitions have been assigned and fitted up to J′ = 35 and K_a′ = 14 using the Watson’s A-reduced Hamiltonian in the I^r representation. Upper state (ν₂= 2) rovibrational constants inclusive of three rotational and five quartic centrifugal distortion constants were accurately determined for the first time. The band center of the 2ν₂ band was determined as 3385.200666 ± 0.000035 cm⁻¹. The rms deviation of the rovibrational fit was 0.00093 cm⁻¹. From the fitting of 451 ground state combination differences (GSCDs) of D₂¹²CO which were derived from the infrared transitions of the 2ν₂ band of this work, together with 360 microwave frequencies from a previous study, new and accurate ground state constants of D₂¹²CO up to three octic terms were obtained. The combination and overtone bands and the newly assigned high-resolution infrared lines of the 2ν₂ band in the 2500–4500 cm⁻¹ region can be used to detect D₂¹²CO in this infrared region. In addition, the results derived from this study give information on the rovibrational molecular structure of D₂¹²CO.

An absorption spectrum of H₂¹⁶O at 1950 K is recorded in a premixed methane/air flat flame using a cavity-enhanced optical frequency comb-based Fourier transform spectrometer. 2417 absorption lines are identified in the 6250–6670 cm^-1 region with an accuracy of about 0.01 cm^-1. Absolute line intensities are retrieved using temperature and concentration values obtained by tunable diode laser absorption spectroscopy. Line assignments are made using a combination of empirically known energy levels and predictions from the new POKAZATEL variational line list. 2030 of the observed lines are assigned to 2937 transitions, once blends are taken into account. 126 new energy levels of H₂¹⁶O are identified. The assigned transitions belong to 136 bands and span rotational states up to J=27.

The water vapour line broadening and shifting for 97 lines in the ν₁ + ν₂ + ν₃ band induced by hydrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm⁻¹ and in a wide pressure range of H₂. The calculations of the broadening γ and shift δ coefficients were performed in the semi-classical method framework with use of an effective vibrationally depended interaction potential. Two potential parameters were optimised to improve the quality of calculations. Good agreements with measured broadening coefficients were achieved. The comparison of calculated broadening coefficients γ with the previous measurements is discussed. The analytical expressions that reproduce these coefficients for rotational, ν₂, ν₁, and ν₃ vibrational bands are presented.

Transition  intensities  for  small  molecules  such  as water and CO₂ can now be computed with such high accuracy  that  they  are  being  used  to  systematically replace  measurements  in  standard  databases.  These calculations use high-accuracy ab initio dipole moment surfaces  and  wave  functions  from  spectroscopically determined  potential  energy  surfaces  (PESs).  Here, an  extra  high-accuracy  PES  of  the  water  molecule (H₂¹⁶O)  is  produced  starting  from  an ab  initio PES which is then refined to empirical rovibrational energy levels.  Variational  nuclear  motion  calculations  using this   PES   reproduce   the   fitted   energy   levels   with a  standard  deviation  of  0.011 cm−1,  approximately three   times   their   stated   uncertainty.   The   use   of wave  functions  computed  with  this  refined  PES  is found to improve the predicted transition intensities for  selected  (problematic)  transitions.  A  new  room temperature  line  list  for  H216O  is  presented.  It  is suggested that the associated set of line intensities is the most accurate available to date for this species.

The remote method of simultaneous determination of the temperature and concentration of hot gases from experimental spectral characteristics is validated on the example of the transmission spectra of water vapor measured with an average error of 5% at temperatures in the range 500–1770 K and concentrations 0.17–1 atm with resolution of 1 cm^–1. When solving the direct optical problem, the parameters of water vapor spectral lines comprised in the HITEMP2010 database are analyzed with allowance for the last measurements of the absorption spectra with high resolution at Т ≈ 1300 K. It is demonstrated that overestimated values of the intensities of some hot water vapor spectral lines can be a reason for the deviation of the theoretical absorption predicted on the basis of the HITEMP2010 database from the experimental one. To increase the accuracy of solving the inverse optical problem, the data from several (up to eight) fragments of the spectral ranges 1000–2500 and 2600–4400 cm^–1 are used. As a result, it is demonstrated that this allows the average error of determining reference values of the water vapor temperature and concentration to be decreased approximately to 0.3%, which corresponds to the average approximation error of theoretical values of its transmission function.

Collision-induced absorption is the phenomenon in which interactions between colliding molecules lead to absorption of light, even for transitions that are forbidden for the isolated molecules. Collision-induced absorption contributes to the atmospheric heat balance and is important for the electronic excitations of O₂ that are used for remote sensing. Here, we present a theoretical study of five vibronic transitions in O₂-O₂ and O₂-N₂, using analytical models and numerical quantum scattering calculations. We unambiguously identify the underlying absorption mechanism, which is shown to depend explicitly on the collision partner-contrary to textbook knowledge. This explains experimentally observed qualitative differences between O₂-O₂ and O₂-N₂ collisions in the overall intensity, line shape and vibrational dependence of the absorption spectrum. It is shown that these results can be used to discriminate between conflicting experimental data and even to identify unphysical results, thus impacting future experimental studies and atmospheric applications.

Quantum mechanical calculations of ro-vibrational energies of CH₄, CHD₃, CH₃D, and CH₃F were made with two different numerical approaches. Both use polyspherical coordinates. The computed energy levels agree, confirming the accuracy of the methods. In the first approach, for all the molecules, the coordinates are defined using three Radau vectors for the CH₃ subsystem and a Jacobi vector between the remaining atom and the centre of mass of CH₃. Euler angles specifying the orientation of a frame attached to CH₃ with respect to a frame attached to the Jacobi vector are used as vibrational coordinates. A direct product potential-optimized discrete variable vibrational basis is used to build a Hamiltonian matrix. Ro-vibrational energies are computed using a re-started Arnoldi eigensolver. In the second approach, the coordinates are the spherical coordinates associated with four Radau vectors or three Radau vectors and a Jacobi vector, and the frame is an Eckart frame. Vibrational basis functions are products of contracted stretch and bend functions, and eigenvalues are computed with the Lanczos algorithm. For CH₄, CHD₃, and CH₃D, we report the first J > 0 energy levels computed on the Wang-Carrington potential energy surface [X.-G. Wang and T. Carrington, J. Chem. Phys. 141(15), 154106 (2014)]. For CH₃F, the potential energy surface of Zhao et al. [J. Chem. Phys. 144, 204302 (2016)] was used. All the results are in good agreement with experimental data.

The ν₃ C–H stretching region of methane was reinvestigated in this work using high temperature (620-1715 K) emission spectra recorded in Rennes at Doppler limited resolution. This work follows our recent global analysis of the Dyad system Δn = ±1 (1000–1500 cm⁻¹), with n being the polyad number [B. Amyay et al., J. Chem. Phys. 144, 24312 (2016)]. Thanks to the high temperature, new assignments of vibration-rotation methane line positions have been achieved successfully in the Pentad system and some associated hot bands (Δn = ±2) observed in the spectral region 2600-3300 cm⁻¹. In particular, rotational assignments in the cold band [Pentad-ground state (GS)] and in the first related hot band (Octad-Dyad) were extended up to J = 30 and 27, respectively. In addition, 1525 new transitions belonging to the Tetradecad-Pentad hot band system were assigned for the first time, up to J = 20. The effective global model used to deal with the new assignments was developed to the 6th order for the first three polyads (Monad, Dyad, and Pentad), and to the 5th order for both the Octad and the Tetradecad. 1306 effective parameters were fitted with a dimensionless standard deviation σ = 2.64. The root mean square deviations dRMS obtained are 4.18 × 10⁻³ cm⁻¹ for the Pentad-GS cold band, 2.48 × 10⁻³ cm⁻¹ for the Octad-Dyad, and 1.43 × 10⁻³ cm⁻¹ for the Tetradecad-Pentad hot bands.

Doppler-free saturated-absorption Lamb dips were measured at sub-Pa pressures on rovibrational lines of H2¹⁶O near 7180 cm⁻¹, using optical feedback frequency stabilized cavity ring-down spectroscopy. The saturation of the considered lines is so high that at the early stage of the ring down, the cavity loss rate remains unaffected by the absorption. By referencing the laser source to an optical frequency comb, transition frequencies are determined down to 100 Hz precision and kHz accuracy. The developed setup allows resolving highly K-type blended doublets separated by about 10 MHz (to be compared to a HWHM Doppler width on the order of 300 MHz). A comparison with the most recent spectroscopic databases is discussed. The determined K-type splittings are found to be very well predicted by the most recent variational calculations.

Molecular hydrogen and its isotopic and ionic species are benchmark systems for testing quantum chemical theory. Advances in molecular energy structure calculations enable the experimental verification of quantum electrodynamics and potentially a determination of the proton charge radius from H2 spectroscopy. We measure the ground state energy in ortho-H2 relative to the first electronically excited state by Ramsey-comb laser spectroscopy on the EF1Σ+g−X1Σ+g(0,0) Q1 transition. The resulting transition frequency of 2 971 234 992 965(73) kHz is 2 orders of magnitude more accurate than previous measurements. This paves the way for a considerably improved determination of the dissociation energy (D0) for fundamental tests with molecular hydrogen.

A model presented in an accompanying work predicts that mid-IR absorption signals from methane in trace concentrations in various buffer gases detected at pressures in the 1–100 Torr range can be reduced and distorted due to depletion of the vibrational ground state if the molecules are exposed to laser powers in the tens of mW range or above. This work provides experimental evidence of such depletion in a resonant cavity under a variety of conditions, e.g. for intracavity laser powers up to 2 W and for buffer gases of N₂ or dry air, and verifies the applicability of the model. It was found that the degree of depletion is significantly larger in N₂ than dry air, and that it increases with pressure for pressures up to around 10 Torr (attributed to a decreased diffusion rate) but decreases with pressure for pressures above 20 Torr (caused by an increased collisional vibrational decay rate). The maximum degree of depletion (∼80%) was obtained for methane in N₂ at around 15 Torr. This implies that absorption spectrometry of methane can experience significant non-linear dependencies on laser power, pressure, as well as buffer gas composition. It is shown that depletion takes place also in ¹³CH₄, which verifies the applicability of the model also for this isotopologue, and that NICE-OHMS signals detected in absorption phase are less affected by depletion than in dispersion. It was concluded that the absorption mode of detection can provide concentration assessments that are virtually free of influence of depletion for intracavity powers below 0.8 W.

We measure speed-dependent Voigt lineshape parameters with temperature-dependence exponents for several hundred spectroscopic features of pure water spanning 6801–7188 cm⁻¹. The parameters are extracted from broad bandwidth, high-resolution dual frequency comb absorption spectra with multispectrum fitting techniques. The data encompass 25 spectra ranging from 296 K to 1305 K and 1 to 17 Torr of pure water vapor. We present the extracted parameters, compare them to published data, and present speed-dependence, self-shift, and self-broadening temperature-dependent parameters for the first time. Lineshape data is extracted using a quadratic speed-dependent Voigt profile and a single self-broadening power law temperature-dependence exponent over the entire temperature range. The results represent an important step toward a new high-temperature database using advanced lineshape profiles.

The germane molecule, GeH₄, is present in the atmospheres of giant planets Jupiter and Saturn. The ongoing NASA mission Juno has renewed interest in its spectroscopy, whose accurate modeling is essential for the retrieval of other tropospheric species. We present here the first complete analysis and modeling of line positions and intensities in the strongly absorbing ν₁/ν₃ stretching dyad region near 2100 cm^-1 for all five germane isotopologues in natural abundance. New infrared spectra were recorded, absolute intensities were extracted through a careful procedure and modeled thanks to the formalism and programs developed in the Dijon group. A database of calculated germane lines, GeCaSDa, has been build and is available online through the Virtual Atomic and Molecular Data Centre (VAMDC) portal and at http://vamdc.icb.cnrs.fr/PHP/gecasda.php.

The infrared spectra of GeH₄ (88.1 % of ⁷⁶GeH₄, 11.5 % of ⁷⁴GeH₄, and a minor amounts of three other stable isotopic species in the sample) were measured in the 4000–4250 cm^-1 region with a high resolution of 0.003 cm^-1 at different pressures with the Bruker IFS 125HR Fourier transform interferometer (Nizhny Novgorod, Russia) and were analyzed theoretically. The 1974 transitions with J^max. = 21 were assigned to the bands ν₁+ν₃(F₂)  and 2ν₁(A₁) of the ⁷⁶GeH₄ isotopologue. Rotational, centrifugal distortion, tetrahedral splitting, and interaction parameters for the (1010, F₂) and (2000, A₁) vibrational states were determined from the fit of experimental line positions. Influence of the (0020, A₁), (0020, E) and (0020, F₂) vibrational states on the structure of the states (1010, F₂) and (2000, A₁) is taken into account. In this case, the main resonance interaction parameters have been estimated on the basis of the local mode model and then fitted. A set of spectroscopic parameters of the effective Hamiltonian obtained from a weighted fit reproduces the initial experimental data with the d_rms=4.5*10^-4 cm^-1. The results of analogous analysis of the ⁷⁴GeH₄ isotopologue (the number of assigned transitions is 652) are presented also.

Water lines in the infrared are convenient frequency references. We present absolute positions of several H₂¹⁶O ro-vibrational transitions around 790 nm using comb-locked cavity ring-down saturation spectroscopy. Lamb dips of 6 water lines with saturation power in the range of 70–130 kW/cm² were observed and the line positions were determined with an accuracy of 25 kHz, corresponding to a fractional uncertainty of 6.6 × 10⁻¹¹. The present work demonstrates the capability to considerably improve the accuracy of the water line positions in the infrared.

The intensity and temperature dependence of four CO2 collision induced absorption (CIA) bands in two spectral regions, 1100–1600 cm^-1 and 2500^-1 have been investigated. The measurements have been performed with a Fourier Transform InfraRed (FT-IR) spectrometer operating in a wide spectral range, from 350 to 25000 cm^-1 (0.4 to 28.5 µm) with a spectral resolution of 2 cm^-1 interfaced with a high pressure-high temperature (HP-HT) absorption cell with an optical path of about 2 cm. While the integrated band intensity of allowed bands shows a linear dependence versus density, the collision-induced integrated band intensity increases quadratically with the density, due to the absorption by pairs of molecules, which allows identifying the CIA bands unambiguously. While below 300 K the binary integrated absorption coefficients exhibit a pronounced temperature dependence due to the presence of dimers, a much weaker temperature dependence has been found above 300 K. The results are important for the radiative transfer calculations of Venus’ atmosphere. The integrated band intensities of the studied bands have been calculated for Venus’ atmosphere from 40 km down to the surface by extrapolating the binary integrated absorption coefficients to the relevant temperatures.

Accurate intensity measurements were performed for several lines of the two main isotopologues of carbon dioxide, using cavity ring down spectroscopy. Absorption spectra of the R52e line at 6112.8902 cm^-1 (30014←00001 band) of ¹²CO₂ and the P6e line at 6114.8580 cm⁻¹ (30013←00001 band) of ¹³CO₂ were recorded at pressures between 15 and 50 mbar at 298 K. Line shape analysis shows that Galatry profile, taking into account Dicke narrowing of spectral lines, better describes the measured spectra at all pressures than the Voigt profile. The values of Dicke narrowing parameter for both lines were found to be significantly smaller than those predicted based on the mass diffusion constant. The values of the line strength for R52e line of ¹²CO₂ and P6e line of ¹³CO₂ were determined with an uncertainty of 0.5%. These values were found to be in good agreement with the corresponding data available in literature, in particular with the most recent ab initio calculations. The results of relative isotopic ratio ¹³CO₂/¹²CO₂ measurements are also presented in pure carbon dioxide samples and in 400 µmol/mol carbon dioxide in air samples, using cavity ring down spectroscopy.

Broadband precision spectroscopy is indispensable for providing high fidelity molecular parameters for spectroscopic databases. We have recently shown that mechanical Fourier transform spectrometers based on optical frequency combs can measure broadband high-resolution molecular spectra undistorted by the instrumental line shape (ILS) and with a highly precise frequency scale provided by the comb. The accurate measurement of the power of the comb modes interacting with the molecular sample was achieved by acquiring single-burst interferograms with nominal resolution matched to the comb mode spacing. Here we describe in detail the experimental and numerical steps needed to achieve sub-nominal resolution and retrieve ILS-free molecular spectra, i.e. with ILS-induced distortion below the noise level. We investigate the accuracy of the transition line centers retrieved by fitting to the absorption lines measured using this method. We verify the performance by measuring an ILS-free cavity-enhanced low-pressure spectrum of the 3ν₁ + ν₃ band of CO₂ around 1575 nm with line widths narrower than the nominal resolution. We observe and quantify collisional narrowing of absorption line shape, for the first time with a comb-based spectroscopic technique. Thus retrieval of line shape parameters with accuracy not limited by the Voigt profile is now possible for entire absorption bands acquired simultaneously.

Rotation-vibration  energy  levels  are  determined  for  the  electronic  ground  state  of  the acetylene  molecule, ¹²C₂H₂,  using  the  Measured  Active  Rotational-Vibrational Energy Levels (MARVEL) technique. 37,813 measured transitions from 61 publications are considered.  The distinct components of the spectroscopic network linking ortho and para states are considered separately. The 20,717 ortho and 17,096 para transitions measured experimentally are used to determine 6013 ortho and 5200 para energy levels. The MARVEL results are compared with alternative compilations based on the use of effective Hamiltonians.

Vacuum-ultraviolet (VUV) photoabsorption spectra were recorded of the A ²Σ⁺(v'=0) <-- X ²Π(v"=0), D ²Σ⁺(v'=0) <-- X ²Π(v"=0) and D ²Σ⁺(v'=1) <-- X ²Π(v"=0) bands of the OH and OD radicals generated in a plasma-discharge source using synchrotron radiation as a background continuum coupled with the VUV Fourier-transform spectrometer on the DESIRS beamline of synchrotron SOLEIL. High-resolution spectra permitted the quantification of transition frequencies, relative f-values, and natural line broadening. The f-values were absolutely calibrated with respect to a previous measurement of A ²Σ⁺(v'=0) <-- X ²Π(v"=0) (Wang et al., 1979). Lifetime broadening of the excited D ²Σ⁺(v'=0) and D ²Σ⁺(v'=1) levels is measured for the first time and compared with previous experimental limits, and implies a lifetime 5 times shorter than a theoretical prediction (van der Loo and Groenenboom, 2005). A local perturbation of the level in OH was found.

High-resolution Fourier transform spectra of the asymmetric methyl- bending and methyl-stretching bands of CH₃SH have been recorded employing synchrotron radiation at the FIR beamline of the Canadian Light Source. Analysis of the torsion-rotation structure and relative intensities has revealed the novel feature that for both bend and stretch the in-plane and out-of-plane modes behave much like a Coriolis-coupled l-doublet pair originating from degenerate E modes of a symmetric top. As the axial angular momentum K increases, the energies of the coupled “l = ±1” modes diverge linearly, with effective Coriolis ξ constants typical for symmetric tops. For the methyl-stretching states, separated at K = 0 by only about 1 cm⁻¹, the assigned sub-bands follow a symmetric top Δ(K – l) = 0 selection rule, with only ΔK = –1 transitions observed to the upper l = –1 in-plane A′ component and only ΔK = +1 transitions to the lower l = +1 out-of-plane A′′ component. The K = 0 separation for the CH₃-bending states is larger at 9.1 cm⁻¹ with the l-ordering reversed. Here, both ΔK = +1 and ΔK = –1 transitions are seen for each l-component but with a large difference in relative intensity. Term values for the excited state levels have been fitted to J(J + 1) power-series expansions to obtain substate origins. These have then been fitted to a Fourier model to characterize the torsion-K-rotation energy patterns. For both pairs of vibrational states, the torsional energies display the customary oscillatory behaviour as a function of K and have inverted torsional splittings relative to the ground state. The spectra show numerous perturbations, indicating local resonances with the underlying bath of high torsional levels and vibrational combination and overtone states. The overall structure of the two pairs of bands represents a new regime in which the vibrational energy separations, torsional splittings and shifts due to molecular asymmetry are all of the same order, creating a challenging and complex vibration-torsion-rotation coupling environment.

A ¹³C-enriched spectrum of methane (¹³CH₄) was recorded at Doppler-limited resolution (0.0044 cm⁻¹) at 80 K covering the entire Tetradecad region in the 4970–6200 cm⁻¹. In this paper we present the spectral analysis of the lower part of the ¹³CH₄ Tetradecad in the 4970–5470 cm⁻¹ region. Starting with a non-empirical effective Hamiltonian derived by high-order Contact Transformations (CT) from the ab initio potential energy surface (PES), the effective Hamiltonian parameters have been determined for this region by extending the previous DAS (Differential Absorption Spectroscopy) spectral analysis for the upper part of the Tetradecad in the 5853–6200 cm⁻¹ region. In total, 1387 rovibrational transitions were assigned belonging to five cold bands of the Tetradecad up to J_max = 11. Their positions were fitted with an rms deviation of 1.6 × 10⁻³ cm⁻¹. Measured line intensities for 737 transitions were modeled using the effective dipole transition moments approach with an rms deviation of about 10%. Finally, the observed transitions were incorporated to fit simultaneously the ¹³CH₄ Hamiltonian parameters for the {Ground state / Dyad / Pentad / Octad / Tetradecad} system and the dipole moment parameters for the {Ground state - Tetradecad} system.

To improve the understanding of temperature-dependence laws of spectral line shape parameters, spectra of the ν₃ rovibrational band of CO₂ perturbed by 10, 30, 100, 300 and 1000 mbar of N₂ were recorded at nine temperatures between 190 K and 330 K using a 22 cm long single-pass absorption cell in a Bruker IFS125 HR Fourier Transform spectrometer. The spectra were fitted employing a quadratic speed-dependent hard collision model in the Hartmann–Tran implementation extended to account for line mixing in the Rosenkranz approximation by means of a multispectrum fitting approach developed at DLR. This enables high accuracy parameter retrievals to reproduce the spectra down to noise level and we present the behavior of line widths, shifts, speed-dependence-, collisional narrowing- and line mixing-parameters over this 140 K temperature range.

Approximately seventy isolated and overlapping methane absorption lines in the 5647 − 6164 cm⁻¹ spectral region were processed with seven line profiles accounting for all main line shape forming physical mechanisms in different combinations. It was shown that at low methane pressures the conventional Nelkin–Ghatak line profile gives satisfactory results in retrieving line parameters as opposed to the Voigt profile. It was found that most of the considered lines do not interfere. The FTS instrumental function elimination technique based on Doppler-broadened line's records was applied, and its applicability was proved.

We report experimental measurements of spectral line shape parameters (air-broadened width, shift, and line mixing coefficients) for several transitions in the ν₃ Q branch of methane in the 3000–3023 cm⁻¹ region. 13 high-resolution, room temperature laboratory spectra of pure methane and air-broadened methane recorded with two different Fourier transform spectrometers are fitted. 12 of these spectra were acquired at 0.01 cm⁻¹ resolution with the McMath-Pierce FTS at the National Solar Observatory on Kitt Peak, and one higher-resolution (∼0.0011 cm⁻¹) low pressure methane spectrum was obtained with the Bruker IFS-120HR FTS at the Pacific Northwest National Laboratory, in Richland, Washington. All the spectra were obtained using high purity natural samples of CH₄ and lean mixtures of the same natural CH₄ in dry air. For the 12 spectra recorded at Kitt Peak, three different absorption cells (L = 5, 25 and 150 cm) were used while the methane spectrum at PNNL was obtained using a 19.95 cm long absorption cell. For the analysis, an interactive multispectrum nonlinear least squares fitting software was employed where all the 13 spectra were fitted simultaneously. An accurate and self-consistent set of line parameters were determined by constraining a few of those for severely blended transitions. Line mixing was measured for 14 transition pairs for the CH₄-air collision system. A constant speed dependence parameter, consistent with measured speed dependence values obtained in other methane bands, was applied to all the transitions included in the fitted region. The present measurements are compared to values reported in the literatur

In this work, we show that precise predictions of the shapes of H₂O rovibrational lines broadened by N₂, over a wide pressure range, can be made using simulations corrected by a single measurement. For that, we use the partially-correlated speed-dependent Keilson–Storer (pcsdKS) model whose parameters are deduced from molecular dynamics simulations and semi-classical calculations. This model takes into account the collision-induced velocity-changes effects, the speed dependences of the collisional line width and shift as well as the correlation between velocity and internal-state changes. For each considered transition, the model is corrected by using a parameter deduced from its broadening coefficient measured for a single pressure. The corrected-pcsdKS model is then used to simulate spectra for a wide pressure range. Direct comparisons of the corrected-pcsdKS calculated and measured spectra of 5 rovibrational lines of H₂O for various pressures, from 0.1 to 1.2 atm, show very good agreements. Their maximum differences are in most cases well below 1%, much smaller than residuals obtained when fitting the measurements with the Voigt line shape. This shows that the present procedure can be used to predict H₂O line shapes for various pressure conditions and thus the simulated spectra can be used to deduce the refined line-shape parameters to complete spectroscopic databases, in the absence of relevant experimental values.

We propose a novel approach to cavity-ring-down-spectroscopy (CRDS) in which spectra acquired with a frequency-agile rapid-scanning (FARS) scheme, i.e., with a laser sideband stepped across the modes of a high-finesse cavity, are interleaved with one another by a sub-millisecond readjustment of the cavity length. This brings to time acquisitions below 20 s for few-GHz-wide spectra composed of a very high number of spectral points, typically 3200. Thanks to the signal-to-noise ratio easily in excess of 10 000, each FARS-CRDS spectrum is shown to be sufficient to determine the line-centre frequency of a Doppler broadened line with a precision of 2 parts over 1011, thus very close to that of sub-Doppler regimes and in a few-seconds time scale. The referencing of the probe laser to a frequency comb provides absolute accuracy and long-term reproducibility to the spectrometer and makes it a powerful tool for precision spectroscopy and line-shape analysis. The experimental approach is discussed in detail together with experimental precision and accuracy tests on the (30 012) ← (00 001) P12e line of CO₂ at ∼1.57 μm.

In this work the high resolution synchrotron radiation Fourier transform spectrum in the range1180-1300 cm^-1 corresponding to the COH- bending vibrational mode has been recorded and analyzed. The spectrum shows a structure analogous to a parallel band. Since the COH bending motion is one of the main contributors to the asymmetry in the torsional hindering potential barrier, the torsional barrier height in the excited state is expected to be quite different from that of the ground state. This makes the spectrum to spread over a wide region. Although the spectrum corresponding to the P- and R- branch looks very complicated, the Q-branches are well resolved and can be identified without much difficulty. It was possible to assign the spectra for K=0 to 10 for the trans- (e₀) species. The interesting feature of the spectra is the absence of the lines for two other lower lying symmetry species e₁ and o₁. The spectra due to any perpendicular transitions were absent as well. The analysis of the spectrum has been carried out to obtain precise term values and molecular parameters in the excited COH- bending state. The results will be shown valuable to assign similar spectra for the methanol-D₂. This work represents the first reported high resolution study of this illusive vibrational mode in methanol-D₁.

Improved analysis of positions and intensities of phosphine spectral lines in the Octad region 2733-3660 cm⁻¹ is reported. Some 5768 positions and 1752 intensities were modelled with RMS deviations of 0.00185 cm⁻¹ and 10.9%, respectively. Based on an ab initio potential energy surface, the full Hamiltonian of phosphine nuclear motion was reduced to an effective Hamiltonian using high-order Contact Transformations method adapted to polyads of symmetric top AB3-type molecules with a subsequent empirical optimization of parameters. More than 2000 new ro-vibrational lines were assigned that include transitions for all 13 vibrational Octad sublevels. This new fitting of measured positions and intensities considerably improved the accuracy of line parameters in the calculated database. A comparison of our results with experimental spectra of PNNL showed that the new set of line parameters from this work permits better simulation of observed cross-sections than HITRAN2012 linelist. In the 2733-3660 cm⁻¹ range, our integrated intensities show a good consistency with recent ab initio variational calculations.

For high-precision determination of the rotational-vibrational energies of the ground vibrational state of the SiH₄ molecule, high-resolution rotational-vibrational spectrum of this molecule in the range 600–1200 cm^–1 in which bands of the ν₂/ ν₄ dyad are located is analyzed. As a result, rotational and centrifugal distortion parameters of the ground vibrational state with a root-mean-square deviation of 2·10^–4 cm^–1 are obtained.

Absorption and emission spectra of carbon dioxide are measured and analyzed for temperatures 220–2500 K in the spectral range 1–25 μm. Intensities and half-widths of the spectral lines are determined and hightemperature atlas of the spectral lines’ parameters is compiled. Based on the developed mathematical model, the parameters of spectral transmission functions of СО₂ are obtained at different temperatures in the vibration-rotation and pressure-induced bands of СО₂. Practical application of the obtained radiative characteristics is considered for solving problems of radiative heat exchange in planetary atmospheres and high-temperature media and designing optoelectronic systems intended for aero carriers monitoring.

Further development of the asymptotic line wing theory is presented where the long-wave approximation for the molecular centers of mass is violated. This provides long molecular trajectories going far beyond an elementary volume in the case of nonresonance light absorption. The occurrence of long trajectories is evidence for a certain degree of ordering of molecular chaos. The latter can be described by means of a modified semiclassical representation method to establish correlation between the displacement and velocity operators. An expression for the absorption coefficient is derived that allows an ambiguity concerning the estimation of the parameters of the potentials to be avoided, and the temperature dependence of the absorption coefficient in line wings to be described. In our earlier work, calculations of the absorption coefficient were performed with violation of the long-wave approximation for molecular centers of mass for H₂O molecule in the 8–12 μm region using a diffusion model. This model is also employed in the present work for H₂O absorption in the 3–5 μm window regions and for CO₂ absorption in the 4.3-μm band wing to describe the temperature dependence of the absorption coefficient. Long molecular trajectories essential for the 8–12 and 3–5 μm H₂O regions are shown to hardly play a role in the 4.3-μm CO₂ band wing.

An analysis of the high-resolution vibrational-rotational IR spectrum of ν₂ + ν₄ (F₁) and ν₂ + ν₄ (F₂) bending absorption bands of the ²⁸SiH₄ molecule is carried out for the first time using the SPHETOM software. Approximately 618 experimental transitions with J_max = 8 are assigned to ν₂ + ν₄ (F₁) and ν₂ + ν₄ (F₂) bands. Rotational, centrifugal distortion, tetrahedral splitting, and resonance interaction parameters for these vibrational bands are derived from the weighted fit of experimental line positions. The set of parameters obtained reproduces the initial experimental data with an accuracy close to the experimental uncertainties d_rms = 8 × 10^–4 cm^–1.

We examine the main sources of uncertainties when measuring the near-infrared water vapor continuum absorption with the Fourier spectrometer complex of the Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences. The instrumental and methodical errors are considered, including errors in determination of the baseline, as well as possible impact of nanoscale complexes of water molecules.

We report the results of an experimental study related to the relaxation of the nuclear spin isomers of the water molecule in a supersonic expansion. Rovibrational lines of both ortho- and para- spin isomers were recorded in the spectral range of H₂O stretching vibrations around 3700 cm(-1) using FTIR direct absorption. Water vapor seeded either in argon, helium, oxygen or in a mixture of oxygen and argon was expanded into vacuum through a slit nozzle. Partial water vapor pressure in the mixture varied in a wide range from 1.5 to 112.7 hPa, corresponding to a water molar fraction evolving between 0.2 and 6.5%. Depending on expansion condition, the effect of water vapor aggregation was clearly seen in some of our measured spectra. The Boltzmann-plot of the lines intensities made possible the determination of the H₂O rotational temperatures in the isentropic core and in the lateral shear layer probed zones of the planar expansion. The study of the OPR, i.e the ratio of the ortho- to para- absorption line intensities as a function of Trot, did not reveal any signs of the OPR relaxed to the sample temperature. In contrast, the OPR was always conserved in agreement with the stagnation reservoir equilibrium temperature. The conservation of the OPR was found irrespective of whether water molecules aggregation was pronounced or not. Also no effect of the paramagnetic oxygen admixture on enhancing the OPR relaxation was observed.

Comprehensive line lists for phosphorus monoxide (³¹P¹⁶O) and phosphorus monosulphide (³¹P³²S) in their X²Π electronic ground state are presented. The line lists are based on new ab initio potential energy (PEC), spin–orbit (SOC) and dipole moment (DMC) curves computed using the MRCI+Q−r method with aug-cc-pwCV5Z and aug-cc-pV5Z basis sets. The nuclear motion equations (i.e. the rovibronic Schrödinger equations for each molecule) are solved using the program duo. The PECs and SOCs are refined in least-squares fits to available experimental data. Partition functions, Q(T), are computed up to T = 5000 K, the range of validity of the line lists. These line lists are the most comprehensive available for either molecule. The characteristically sharp peak of the Q-branches from the spin–orbit split components gives useful diagnostics for both PO and PS in spectra at infrared wavelengths. These line lists should prove useful for analysing observations and setting up models of environments such as brown dwarfs, low-mass stars, O-rich circumstellar regions and potentially for exoplanetary retrievals. Since PS is yet to be detected in space, the role of the two lowest excited electronic states (a⁴Π and B²Π) are also considered. An approximate line list for the PS X–B electronic transition, which predicts a number of sharp vibrational bands in the near ultraviolet, is also presented. The line lists are available from the CDS (http://cdsarc.u-strasbg.fr) and ExoMol (www.exomol.com) data bases.

An extended E⊗e Jahn-Teller Hamiltonian is presented for the case where the (slow) nuclear motion extends far from the symmetry point and may be described approximately as motion on a sphere. Rather than the traditional power series expansion in the displacement from the C_3v symmetry point, an expansion in the spherical harmonics is employed. Application is made to the vibrational Jahn-Teller effect in CH₃XH, with X = S, O, where the equilibrium CXH angles are 83° and 72°, respectively. In addition to the symmetry-required conical intersection (CI) at the C_3v symmetry point, ab initio calculations reveal sets of six symmetry-allowed vibrational CIs in each molecule. The CIs for each molecule are arranged differently in the large-amplitude space, and that difference is reflected in the infrared spectra. The CIs in CH₃SH are found in both eclipsed and staggered geometries, whereas those for CH₃OH are found only in the eclipsed geometry near the torsional saddle point. This difference between the two molecules is reflected in the respective high-resolution spectra in the CH stretch fundamental region.

In analyzing high-resolution spectra of the methyl-deformation bands of methyl mercaptan recorded at the Canadian Light Source synchrotron, we have encountered interesting interactions between certain levels of the ν₄ in-plane asymmetric CH₃-bending mode and its ν₁₀ out-of-plane bending partner below. The origin of the K = 0 A ν₄ substate is just 0.2 cm⁻¹ higher than that of the K = 2A ν₁₀ substate, while the K = 0 E ν₄ origin is only 0.035 cm⁻¹ below the K = 2E ν₁₀ origin. These very close accidental near-degeneracies lead to substantial perturbations in the spectrum. For the former, the A⁺/A– asymmetry K-doublet coupling rules are such that the A– component of the 2A ν10 doublet interacts and mixes strongly with the 0A⁺ ν₄ levels whereas the 2A⁺ component is unaffected. The 2A– levels are pushed rapidly downwards by the coupling creating an extremely large apparent K = 2A asymmetry splitting. We call this “giant K-doubling” by analogy with a comparable phenomenon seen for methanol. The 0A⁺ ν₄ state, in turn, is perturbed upward and passes through the descending K=1A⁺ ν₄ state between J = 22 and 23, leading to distinct local perturbations near the level-crossing. The 0E ν₄ and 2E ν₁₀ coupling produces a correspondingly strong repulsion and mixing between those two substates, and gives rise to a forbidden K = 0 ← 3E intermode sub-band in the spectrum via intensity borrowing.

We compute four-dimensional diabatic potential energy surfaces and transition dipole moment surfaces of O₂–O₂, relevant for the theoretical description of collision-induced absorption in the forbidden X ³Σ^-_g→ a ¹Δ_g and X ³Σ^-_g→ b ¹Σ⁺_g bands at 7883 cm⁻¹ and 13 122 cm⁻¹, respectively. We compute potentials at the multi-reference configuration interaction (MRCI) level and dipole surfaces at the MRCI and complete active space self-consistent field (CASSCF) levels of theory. Potentials and dipole surfaces are transformed to a diabatic basis using a recent multiple-property-based diabatization algorithm. We discuss the angular expansion of these surfaces, derive the symmetry constraints on the expansion coefficients, and present working equations for determining the expansion coefficients by numerical integration over the angles. We also present an interpolation scheme with exponential extrapolation to both short and large separations, which is used for representing the O₂–O₂ distance dependence of the angular expansion coefficients. For the triplet ground state of the complex, the potential energy surface is in reasonable agreement with previous calculations, whereas global excited state potentials are reported here for the first time. The transition dipole moment surfaces are strongly dependent on the level of theory at which they are calculated, as is also shown here by benchmark calculations at high symmetry geometries. Therefore, ab initio calculations of the collision-induced absorption spectra cannot become quantitatively predictive unless more accurate transition dipole surfaces can be computed. This is left as an open question for method development in electronic structure theory. The calculated potential energy and transition dipole moment surfaces are employed in quantum dynamical calculations of collision-induced absorption spectra reported in Paper II [T. Karman et al., J. Chem. Phys. 147, 084307 (2017)].

We derive the theory of collision-induced absorption for electronic transitions  in the approximation of an isotropic interaction potential. We apply this theory to the spin-forbidden X ³Σ^-_g→ a ¹Δ_g and X ³Σ^-_g → b ¹Σ⁺_g transitions in O₂–O₂, which are relevant for calibration in atmospheric studies. We consider two mechanisms for breaking the spin symmetry, either by the intermolecular exchange interaction between paramagnetic collision partners or by the intramolecular spin-orbit coupling. The calculations for the exchange-based mechanism employ the diabatic potential energy surfaces and transition dipole moment surfaces reported in Paper I [T. Karman et al., J. Chem. Phys. 147, 084306 (2017)]. We show that the line shape of the theoretical absorption spectra is insensitive to the large uncertainty in the electronic transition dipole moment surfaces. We also perform calculations using a simple model of the alternative mechanism involving intramolecular spin-orbit coupling, which leads to absorption intensities which are well below the experimental results. The relative intensity of this spin-orbit-based mechanism may impact the relative contribution to the absorption by collisions with diamagnetic collision partners, such as the atmospherically relevant N2 molecule. We furthermore show that both the line shape and temperature dependence are signatures of the underlying transition mechanism.

Rovibrational states of the four dimers formed by the light and the heavy isotopologues of the methane and the water molecules are computed using a potential energy surface taken from the literature. The general rovibrational energy-level pattern characteristic to all systems studied is analyzed employing two models of a dimer: the rigidly rotating complex and the coupled system of two rigidly rotating monomers. The rigid-rotor model highlights the presence of rovibrational sequences corresponding to formally negative rotational excitation energies, which is explained in terms of the coupled-rotors picture.

Spectroscopy has been crucial for our understanding of physical and chemical phenomena. The interpretation of interstellar line spectra with radiative transfer calculations usually requires two kinds of molecular input data: spectroscopic data (such as energy levels, statistical weights, transition probabilities, etc.) and collision data. This contribution describes how such data are collected, stored, and which limitations exist. Also, here we summarize challenges of atomic/molecular databases and point out our experiences, problems, etc., which we are faced with. We present overview of future developments and needs in the areas of radiative transfer and molecular data.

As an exoplanet transits its host star, some of the light from the star is absorbed by the atoms and molecules in the planet’s atmosphere, causing the planet to seem bigger; plotting the planet’s observed size as a function of the wavelength of the light produces a transmission spectrum. Measuring the tiny variations in the transmission spectrum, together with atmospheric modelling, then gives clues to the properties of the exoplanet’s atmosphere. Chemical species composed of light elements—such as hydrogen, oxygen, carbon, sodium and potassium—have in this way been detected in the atmospheres of several hot giant exoplanets, but molecules composed of heavier elements have thus far proved elusive. Nonetheless, it has been predicted that metal oxides such as titanium oxide (TiO) and vanadium oxide occur in the observable regions of the very hottest exoplanetary atmospheres, causing thermal inversions on the dayside. Here we report the detection of TiO in the atmosphere of the hot-Jupiter planet WASP-19b. Our combined spectrum, with its wide spectral coverage, reveals the presence of TiO (to a confidence level of 7.7σ), a strongly scattering haze (7.4σ) and sodium (3.4σ), and confirms the presence of water (7.9σ) in the atmosphere.

Nitrous oxide (N₂O) is a key greenhouse gas and a major ozone-depleting anthropogenic pollutant monitored by the total carbon column observing network (TCCON) in the 0002-0000-band of its main isotopologue. Here, we present highly accurate line strengths for this window determined using Fourier transform infrared spectroscopy with pressure, temperature, and optical path length being metrologically traceable to the SI. The obtained results agree with previous studies within the given uncertainties. Depending on the respective rovibrational transition, the present uncertainties could be reduced by a factor of 5 to 83 in comparison to literature data.

Transitions of the 6ν3 overtone band of ¹⁴N2¹⁶O near 775 nm have been studied by continuous-wave cavity ring-down spectroscopy. Line positions and intensities were derived from a fit of the line shape using a hard-collisional profile. The line positions determined with absolute accuracy of 5×10⁻⁴ cm⁻¹ allowed us to reveal finer ro-vibrational couplings taking place after J>14 except a strong anharmonic interaction identified by the effective Hamiltonian model. The absolute line intensities have also been retrieved with an estimated accuracy of 2% for a majority of the unblended lines. A new set of ro-vibrational and dipole moment parameters were derived from the experimental values. A comparison between the line positions and intensities of the 6ν3 band obtained in this work and those from previous studies is given.

The infrared spectra of SiH4 in natural abundance (92.23% of ²⁸SiH₄, 4.68% of ²⁹SiH₄, and 3.09% of ³⁰SiH₄) were measured in the region of 600–1200 cm⁻¹ with a Bruker IFS 120HR Fourier transform spectrometer, analyzed and compared with the results available in the literature. More than 3500 transitions with were assigned to the dyad bands ν₄ and ν₂ of ²⁸SiH₄ (the band ν₂ is allowed in Raman, but forbidden in absorption spectra for symmetry reasons, and its transitions appear in absorption spectra only because of strong Coriolis interaction with the ν₄ band). Rotational, centrifugal distortion, tetrahedral splitting, and interaction parameters for the ground, (0100) and (0001) vibrational states were determined from the fit of experimental line positions. The obtained set of parameters reproduces the initial experimental data with accuracy close to experimental uncertainties. The results of the analogous analyses of the ²⁹SiH₄ and ³⁰SiH₄ isotopologues are also presented (the numbers of the assigned transitions are here more than 1360 and 1120). An further analysis of about 790 experimental ro-vibrational lines in the dyad region of ²⁸SiH₄ was performed using the Voigt profile to simulate the measured line shape and to determine experimental line intensities. A set of 4 effective dipole moment parameters for the dyad of ²⁸SiH₄ was obtained on that basis from the weighted fit, which reproduce the initial experimental intensities of about 790 lines with the . Analogous analyses were made for the two other isotopic species, ²⁹SiH₄, and ³⁰SiH₄. A detailed line list of transitions in the region of 750–1150 cm⁻¹ is generated. The half-widths of 40 ro-vibrational lines are studied from the multi-spectrum analysis, and self-pressure broadening coefficients are determined.

The 8.5-µm spectral region of methyl fluoride was recently studied in terms of line positions, intensities and self-broadening coefficients at room temperature [JQSRT 2016;185:58–69]. The present work is dedicated to measurements of N₂-broadening coefficients for transitions of the ν₆ band. Based on new set of Fourier transform spectra using various mixtures of CH₃F and N₂, a multispectrum fitting procedure was used to retrieve N₂-broadening for 1189 transitions between 1105 and 1291 cm⁻¹. 899 transitions have been studied to model the J- and K-rotational quantum number dependences of the N₂-broadening coefficients in order to generate any transitions of CH₃F assuming no vibrational dependence. The accuracy of the retained N₂-broadening coefficients was estimated to be between 2–5%. These measurements have been compared with previous studies from the literature obtained for other bands of CH₃F. Comparison with the results obtained for similar empirical J- and K-rotational model applied to CH₃Cl, CH₃Br and CH₃F (this work) molecules is also presented.

Six studies have been recently devoted to a systematic analysis of the high-resolution near infrared absorption spectrum of acetylene recorded by Cavity Ring Down spectroscopy (CRDS) in Grenoble and by Fourier-transform spectroscopy (FTS) in Brussels and Hefei. On the basis of these works, in the present contribution, we construct an empirical database for acetylene in the 5850–9415 cm^–1 region excluding the 6341–7000 cm⁻¹ interval corresponding to the very strong ν₁+ν₃ manifold. Our database gathers and extends information included in our CRDS and FTS studies. In particular, the intensities of about 1700 lines measured by CRDS in the 7244–7920 cm⁻¹ region are reported for the first time together with those of several bands of ¹²C¹³CH₂ present in natural isotopic abundance in the acetylene sample.

The Herman-Wallis coefficients of most of the bands are derived from a fit of the measured intensity values. A recommended line list is provided with positions calculated using empirical spectroscopic parameters of the lower and upper energy vibrational levels and intensities calculated using the derived Herman-Wallis coefficients. This approach allows completing the experimental list by adding missing lines and improving poorly determined positions and intensities. As a result the constructed line list includes a total of 11113 transitions belonging to 150 bands of ¹²C₂H₂ and 29 bands of ¹²C¹³CH₂. For comparison the HITRAN database in the same region includes 869 transitions of 14 bands, all belonging to ¹²C₂H₂. Our weakest lines have an intensity on the order of 10^–29 cm/molecule, about three orders of magnitude smaller than the HITRAN intensity cut off. Line profile parameters are added to the line list which is provided in HITRAN format.

The comparison of the acetylene database to the HITRAN2012 line list or to results obtained using the global effective operator approach is discussed in terms of completeness and accuracy.

A new recommended ¹²C₂H₂ line list for the 13–248 cm^–1 and 390–634 cm^–1 regions is presented. It is based on the results of the global modeling of the line positions and intensities performed in Tomsk within the framework of the method of effective operators. To validate the Tomsk calculations new measurements of both line positions and intensities were performed using acetylene spectra recorded between 25 and 680 cm⁻¹ with the AILES-A beamline of SOLEIL synchrotron. Line positions and intensities of 627 transitions belonging to 9 bands have been measured for the first time in this region. Using the results of these new measurements and the published results of the measurements in the 13–248 cm^–1 and 390–634 cm^–1 regions performed with the same facilities new fittings of the line intensities for the ∆P=0 and ∆P=1 series of transitions have been performed. Here P=5v₁+3v₂+5v₃+v₄+v₅ is a polyad number, where v₁, v₂, v₃, v₄, and v₅ are the principal quantum numbers of the acetylene harmonic oscillators. These new sets of the effective dipole moment parameters were used to generate the line list which contains the line positions and intensities of 39 and 29 bands, respectively for the ∆P=0 and ∆P=1 series of transitions. None of these bands is present in the HITRAN 2012 [8] and GEISA 2015 [9] databases. This paper presents the first part of a global work on the validation of Tomsk calculations.

Infrared absorption spectra of NH₃ have been obtained at high resolution (0.02 cm⁻¹) at seven temperatures between 296 and 973 K. The spectra were recorded using a Bruker IFS 125 infrared Fourier transform spectrometer in the 2400–5500 cm⁻¹ region and empirical lower state energies have been obtained by comparison of line strengths at different temperatures. Using two reference line lists, quantum number assignments have been made for each temperature for between 1660 and 3020 transitions, with J up to 22. The line lists obtained provide accurate line positions as well as intensities and experimental lower state energies at temperatures relevant for modeling the atmospheres of brown dwarfs and exoplanets.

The high resolution infrared spectra of the 32S16O18O molecule were recorded for the first time with a Bruker IFS 120 HR Fourier transform interferometer and analysed in the region of 1550–1950 cm⁻¹ where the bands v₁+v₂ and v₂+v₃ are located. About 1050 and 1570 transitions were assigned in the experimental spectra with the maximum values of quantum numbers Jnax/Kamax equal to 64/16 and 58/19 to the bands v₁+v₂ and v₂+v₃, respectively. The subsequent weighted fit of experimentally assigned transitions was made with the Hamiltonian model which takes into account the resonance interactions between the studied vibrational states. As the result, a set of 16 fitted parameters was obtained which reproduces the initial 1442 ro-vibrational energy values obtained from the assigned transitions with the d_rms=6.9%. An analysis of more than 4050 experimental ro-vibrational line intensities of the v₁+v₂ and v₂+v₃ bands of ³²S¹⁶O₂ was made, and a set of 7 effective dipole moment parameters was obtained which reproduce the initial experimental line intensities with the . Values of these parameters, being re-calculated to the values of corresponding parameters of the ³⁴S¹⁶O₂, ³²S¹⁸O₂ and ³²S¹⁶O¹⁸O species were used for calculation of line intensities in the v₁+v₂ and v₂+v₃ bands of these three isotopologues. A list of transitions with their line intensities in the region of 1550–1950 cm⁻¹ for the four mentioned species is generated.

Several Doppler-limited rotational transitions of methane induced by centrifugal distortion have been measured with an unprecedented frequency accuracy using a THz photomixing synthesizer based on a frequency comb. Compared to previous synchrotron based FT-Far-IR measurements of Boudon et al. (Ref. [1]), the accuracy of the line frequency measurements is improved by one order of magnitude; this yields a corresponding increase of two orders of magnitude to the weighting of these transitions in the global fit. The rotational transitions in the v₄ <-- v₄ hot band are measured for the first time by the broad spectral coverage of the photomixing CW-THz spectrometer providing access up to R(5) transitions at 2.6 THz. The new global fit including the present lines has been used to update the methane line list of the HITRAN database. Some small, but significant variations of the parameter values are observed and are accompanied by a reduction of the 1-σ uncertainties on the rotational (B0) and centrifugal distortion (D0) constants.

This manuscript reports an effort to improve the absolute accuracy of ozone intensities in the 10 µm region via a transfer of the precision of the rotational dipole moment onto the infrared measurement. The approach determines the ozone mixing ratio through alternately measuring seven pure rotation ozone lines from 692 to 779 GHz. A multispectrum fitting technique was employed. The results determine the column with absolute accuracy of 1.5% and the intensities of infrared transitions measured at this accuracy reproduce the recommended values to within a standard deviation of 2.8%.

The very weak 4ν₃ B-typeabsorption band of the nitrogen dioxide main isotopologue (¹⁴N¹⁶O₂) is investigated between 6175 and 6350 cm⁻¹. The absorption spectrum of this band was recorded by high sensitivity continuous wave-cavity ring down spectroscopy with noise equivalent absorption of α_min ≈ 1 × 10⁻¹⁰ cm⁻¹. More than 1630 lines of the 4ν₃ band are assigned with rotational quantum numbers N and K_a up to 55 and 7, respectively, what corresponds to 1731 spin-rotation-vibration transitions. The overall measured set of the line positions is used to fit the effective Hamiltonian parameters. The effective Hamiltonian takes explicitly into account the Coriolis interactions between the spin rotational levels of the (0,0,4) vibrational state and those of the nearby (0,2,3) bright state at 6183.61 cm⁻¹ together with the electron spin-rotation interactions. The fitted set of the parameters reproduces the observed line positions with an rms of 2.2 × 10⁻³ cm⁻¹. A selected set of the measured line intensities are used to determine the effective dipole moment parameters including the Herman–Wallis type parameters describing the line intensities of the 4ν₃ band. The rms deviation of the fit is 5.7%.

Modeling atmospheres of hot exoplanets and brown dwarfs requires high-T databases that include methane as the major hydrocarbon. We report a complete theoretical line list of ¹²CH₄ in the infrared range 0–13,400 cm⁻¹ up to T_max = 3000 K computed via a full quantum-mechanical method from ab initio potential energy and dipole moment surfaces. Over 150 billion transitions were generated with the lower rovibrational energy cutoff 33,000 cm⁻¹ and intensity cutoff down to 10⁻³³ cm/molecule to ensure convergent opacity predictions. Empirical corrections for 3.7 million of the strongest transitions permitted line position accuracies of 0.001–0.01 cm⁻¹. Full data are partitioned into two sets. "Light lists" contain strong and medium transitions necessary for an accurate description of sharp features in absorption/emission spectra. For a fast and efficient modeling of quasi-continuum cross sections, billions of tiny lines are compressed in "super-line" libraries according to Rey et al. These combined data will be freely accessible via the TheoReTS information system (http://theorets.univ-reims.fr, http://theorets.tsu.ru), which provides a user-friendly interface for simulations of absorption coefficients, cross-sectional transmittance, and radiance. Comparisons with cold, room, and high-T experimental data show that the data reported here represent the first global theoretical methane lists suitable for high-resolution astrophysical applications.

A new study of ¹²CH₄ line positions and intensities was performed for part of the Tetradecad region between 5300 and 5550 cm⁻¹ using four long path (202 m, 602 m, 1604 m and 1804 m) spectra of normal samples of CH₄ at different pressures recorded with a Fourier transform spectrometer in Reims, France. Line positions and intensities were retrieved by least square curve-fitting procedures and analyzed using the effective Hamiltonian and the effective dipole moment expressed in terms of irreducible tensor operators adapted to spherical top molecules. An 80 K spectrum from JPL of enriched ¹²CH₄ was used for low-J line positions. One other 80 K spectrum from JPL of enriched ¹³CH₄ was used to discern the isotopic lines. A new measured linelist contains positions and intensities for 5934 features. Quantum assignments were made for 2847 transitions, which represent ∼90% of the integrated line intensity observed in this region. All assigned line positions and 2227 selected line intensities were fitted with RMS standard deviations of 0.0025 cm⁻¹ and 8.6%, respectively. The sum of observed intensities between 5300 and 5550 cm⁻¹ fell within 2% of the predicted value from ab initio variational calculations.

High–resolution (0.004 cm ) Fourier transform spectra of the ¹⁵NH2D molecule were recorded for the first time in the region of 1000–1800 cm at LISA in Créteil and analyzed. Assignments of transitions were made on the basis of the Ground State Combination Differences method. Parameters of the effective Hamiltonian of the ground vibrational state in the model of the asymmetric top molecule in reduction and representation were determined from the fit of MW and FIR data known in the literature. As a result of the analysis, about 4380 ro-vibrational transitions have been assigned to the five vibrational states and and the values of 647 upper ro-vibrational energy levels were determined. A weighted fit was carried out using the model of the effective Hamiltonian which takes into account strong resonance interaction between all five upper vibrational states corresponding to the observed and and interaction of these five states with an unobserved sixth state . A set of 168 parameters obtained from the fit provided the basis to reproduce the initial 647 energy values (line positions of about 4380 transitions) of the five mentioned inversion–vibrational states with the d cm .

A study of the vibration-rotation absorption spectrum of the D₂O molecule in the range 10100–10800 cm^-1 has been performed. The spectrum was recorded using a Fourier Transform Spectrometer with the spectral resolution of 0.05 cm^-1 coupled to the multi-pass White-type cell providing an optical path length of 24 m. A light-emitting diode was used as the radiation source, giving a high brightness that resulted in an S/N ratio of measurements of about 10⁴. The rovibrational assignment of more than 920 lines was carried out, and the parameters of the spectral lines (i.e. centers, intensity and half-width) were determined by least-squares fitting of the Voigt contour parameters to the experimental data. A total of 530 rotational energy levels belonging to nine vibrational states (301), (103), (400), (221), (122), (320), (004), (023) and (042) and with maximum rotational quantum numbers J=16 and Ka=9 was determined. 101 energy levels were derived from the experiment for the first time.

Line lists are presented for six deuterated isotopologues of water vapor namely HD¹⁶O, HD¹⁷O, HD¹⁸O, D₂¹⁶O, D₂¹⁷O and D₂¹⁸O. These line lists are prepared using empirically-determined energy levels, where available, to provide transition frequencies and high-quality ab initio dipole moment surfaces to provide transition intensities. The reliability of the predicted intensities is tested by computing multiple line lists and analyzing the stability of the results. The resulting intensities are expected to be accurate to a few percent for well-behaved, stable transitions. Complete 296K line lists are provided for each species.

Lorentz half-width coefficients and their temperature dependence exponents for CO₂ broadening in the fundamental bands of HDO are important for reliable and accurate interpretation of Mars and Venus atmospheric data and to determine D/H. Uncertainties in the temperature dependences of the CO₂-broadened half-width coefficients lead to large errors in the retrieved mixing ratios and hence in HDO column abundances. In this high-resolution FTIR laboratory study, we report first measurements of the temperature dependences of half-width coefficients for HDO transitions in the ν₁ and 2ν₂ bands broadened by CO₂. Accurate line positions, intensities, CO₂-broadened width and pressure shift coefficients, their temperature dependences, collisional line mixing coefficients for HDO-CO₂ system and quadratic speed dependence parameters have been retrieved for a large number of transitions in the ν₁ band. Room-temperature self-broadened half-width coefficients, self-shift coefficients, and collisional line-mixing coefficients for HDO-HDO system were also measured for the same number of ν₁ transitions. Positions and intensities were measured for nearly 60 transitions in the weaker 2ν₂ band along with a few room-temperature measurements of CO₂- and self-broadening and pressure-shift coefficients. These results were obtained from simultaneous nonlinear least squares fittings of ten high-resolution absorption spectra recorded with the Bruker IFS-125HR FTS at JPL and two coolable sample cells. Modified Complex Robert-Bonamy (MCRB) formalism was applied to compute both types of broadening and pressure shift coefficients, and the temperature dependences of the CO₂- and self-broadening parameters. Present measurements are compared with the MCRB calculations and other theoretical values reported in the literature.

A high resolution Fourier transform spectrum of mono-deuterated water vapor was studied between 11,200 and 12,400 cm⁻¹ using a Fourier transform spectrometer with the spectral resolution of 0.05 cm⁻¹, coupled to a multi-pass White-type cell that provided an optical path length of 24 m. A light-emitting diode was used as the radiation source to obtain a measurement signal-to-noise ratio of about 10⁴. The rotational-vibrational assignment of more than 1560 lines was carried out using the VTT variational line list. The parameters of the spectral lines (line centers, intensities and half-widths) were determined by least-squares fitting of the Voigt contour parameters to the experimental data. A total of 584 rotational–vibrational energy levels with maximum rotational quantum numbers of J = 16 and Ka = 9 were determined. For the first time, 64 new energy levels belonging to the nine vibrational states: (032), (112), (301), (141), (410), (221), (330), (061) and (170) were derived from the experiment.

The rotational structure of the (111) and (021) vibrational states is determined for the first time from the high resolution analysis of the v₁+v₂+v₃-v₂ and 2v₂+v₃-v₂ “hot” bands. The 480 and 74 transitions of these bands (J^max= 45/14 and 15/12, respectively) were assigned in the spectra, which have been recorded with the Bruker IFS 120 Fourier transform infrared (FTIR) spectrometer. A weighted fit analysis allowed us to generate a set of 5 fitted parameters for the (111) state and 4 fitted parameters for the (021) state. Calculation with the 9 parameters, obtained from the fit, reproduces the initial 363 energy values (about 550 assigned experimental transitions) of two vibrational states with the drms deviations of 3.2*10^-4 cm^-1 which is comparable with the experimental uncertainties of very weak transitions of the v₁+v₂+v₃-v₂ and 2v₂+v₃-v₂ “hot” bands in our experiment.