The water vapor absorption line resulting from the rotational transition 5-1-6-5 has been investigated experimentally. Radiation is fed into an air-filled cubical copper cavity 8 ft. on an edge. Strings of thermocouples with alternate junctions coated with a "lossy" material are placed at random in the cavity. The e.m.f. of these thermocouples is proportional to the Q of the cavity and its contents. With the total pressure inside the cavity at one atmosphere, the partial pressure of the water vapor is varied from 1 mm to 55 mm of Hg. A measurement of the change in e.m.f. with humidity yields a value for the losses in the water vapor, provided the Q of the cavity is known. This quantity may be determined from additional measurements taken with an aperture opened in the side of the cavity. The wave-length range between 0.7 cm and 1.7 cm has been explored. Results indicate a peak at ν̃=0.744±0.005 cm-1, corresponding to a wave-length λ=1.34 cm. The absorption line is broadened as the water vapor density is increased. At very low density, the half-width of the curve (half-width at half-height) is 0.087±0.01 cm-1, while the corresponding value for a density of 50 gram/meter3 is 0.107±0.01 cm-1. The cross section for a water-water collision must be nearly 5 times that for a water-air collision to account for this change in half-width with vapor density. The attenuation at the peak is 0.025 db per kilometer for 1 gram of water vapor per cubic meter.
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Grating measurements at oblique incidence are employed as a means of obtaining the narrow slits essential to the direct observation of line width. Correction for the finite width of slit is small. It is accomplished by empirical extrapolation to zero slit in one instance, and by numerical estimation of slit influence in another. The absorption coefficient half-width at half-height for the atmospheric water vapor lines at 18.64 μ and 15.99 μ is found to be 0.12 cm-1 and 0.11 cm-1, respectively.
The self- and nitrogen-broadened half-widths and the strengths of three lines in the far i.r. rotational spectrum of water vapor have been measured. These lines are the 21-11 transition at 92 cm-1, the 41-31 transition at 170 cm-1, and the 50-40 transition at 188 cm-1. These are among the very few lines in this region which are sufficiently isolated to be amenable to measurement. The method of equivalent widths, as developed in the Ladenburg-Reiche theory, is used. All measurements are made in a cell of length 21·5 cm. By adding nitrogen at pressures from zero to one atmosphere to water vapor at pressures from 0·5 to 17 mm Hg, these lines may be observed in both the square root and the linear regions of the Ladenburg-Reiche curve. Fitting the data to the asymptotic expansion in the square root region, and to the exact equation in the nearly linear region by a method of successive approximations, the line strengths, self-broadened half-widths, nitrogen-broadened half-widths and relative broadening efficiency is obtained. A new method is introduced to correct for overlap, which is very severe in this region. With the assumption that W/pa, the ratio of the equivalent width to the pressure of the absorber, is constant for the pure water vapor, an equation is obtained for the observed value of this ratio in terms of certain overlap parameters. The resulting line strengths are shown to be in agreement with the calculated values. The self- and nitrogen-broadened half-widths are compared with the calculations made by Benedict and Kaplan on the basis of the Anderson theory. The observed values are larger than the theoretical by a factor of about 1·5.
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The 2+2-->3–2 rotational transition in water vapor has been carefully studied by using both a simple video and a double modulation millimeter wave spectrometer. The line center remeasured is v0 = 183 310.12±0.10 Mc/sec. Self-broadening and foreign-gas broadening were investigated over the pressure range of 5 to 400 µ of Hg with the following results:
These results, obtained by the double modulation spectrometer, have been compared with other line broadening studies, and for the first time linewidth calculations on asymmetric molecules appear to be valid.
The purpose of The Journal of Chemical Physics is to bridge a gap between journals of physics and journals of chemistry by publishing quantitative research based on physical principles and techniques, as applied to "chemical" systems. Just as the fields of chemistry and physics have expanded, so have chemical physics subject areas, which include polymers, materials, surfaces/interfaces, and biological macromolecules, along with the traditional small molecule and condensed phase systems. The Journal of Chemical Physics (JCP) is published four times per month (48 issues per year) by the American Institute of Physics.
Absorption spectra of pure water vapor and mixtures of water vapor with air have been measured, at the wings of the ν2 band, at temperatures of 400°K and 540°K. The vibration-rotation interaction in this band has been measured by the relative intensities of the rotational lines, and the total intensity of the band has been found to be S0v = 265±10 per cent (cm-2 atm-1 at STP). The line widths of the rotational transitions for self broadening have been found to decrease as a function of temperature, and for the broad and strong lines the width is approximately inversely proportional to the absolute temperature.
Optics and Spectroscopy (Optika i spektroskopiya), founded in 1956, presents original and review papers in various fields of modern optics and spectroscopy in the entire wavelength range from radio waves to X-rays. Coverage includes problems of theoretical and experimental spectroscopy of atoms, molecules, and condensed state, lasers and the interaction of laser radiation with matter, physical and geometrical optics, holography and physical principles of optical instrument making.
This paper describes an experimental investigation of the 1.63-mm H2O absorption line for nitrogen-water-vapor mixtures and for oxygen-water-vapor mixtures. Frequency sweep measurements were made at pressures between 1 and 5 mm of mercury and measurements at discrete frequencies were made for pressures between 200 and 760 mm of mercury. These measurements were made over a range of temperatures from 242° to 325°K. Data for the attenuation and line breadth constant as a function of temperature are presented.
The absorption spectrum of water vapor has been studied quantitatively with a resolution of approximately 0.12 cm-1 between 475–692 cm-1. Several methods of extracting the intensity and line-width parameters from the measurements on 19 well-resolved lines are compared and discussed. The intensities show deviations from those calculated for a rigid asymmetric rotor, which are attributed to effects of centrifugal stretching. Half-widths are presented for H2O-H2O, H2O-N2, H2O-CO2, and H2O-He broadening at 80°C and for H2O-air at 24°C.
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A differential microwave refractometer has been found to be an excellent tool for accurate study of foreign-gas broadening of isolated spectral lines. Many experimental and analytic difficulties disappear when foreign gas is admitted at the maximum of a self-broadened dispersion pressure profile. The new principle has been applied to determine the broadening efficiencies for helium, argon, oxygen, hydrogen, nitrogen, acetylene, carbon dioxide, and acetonitrile on the rotational transition Jtau: 5–1 --> 6–5 of water vapor at 22 GHz. The gases chosen represent a wide range in effective collision cross sections, as well as the main atmospheric constituents.
Measurements have been made of the position, width and intensity of the 31-4-3 water-vapour absorption line centred at λ = 0.787 mm. A Froome-type arc harmonic generator provided the high resolution needed to scan the line accurately. By transmitting the harmonic power through an absorption cell 4.8 m long, containing air of known and controlled humidity, it was possible to locate the line centre to within 0.05 %, to measure the line width to within 7% and the molecular dipole moment to within 2.5%. The results are compared with existing theoretical and experimental data.
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Absorption lines in the v, band of water vapor at 6.3 micrometers have been fully resolved by using a tunable semiconductor laser. Three attnospheric water vapor lines near 5.32 micrometers were studied in detail and found to have linle widths two to four times narrower than the width calculated by Benedict and Kaplan.
Using a Froome-type plasma-metal junction harmonic generator, high resolution transmission measurements have been made on the atmosphere in the wavelength range 0.5–3.0 mm. Theoretical spectra have been computed for submillimetre-millimetre wavelength atmospheric absorption due to water vapour using the kinetic equation form for the line shape.
Measurements were made on the basic parameters of the main water vapour absorption lines occurring in the wavelength range 0.65–3.0 mm. The pure water vapour line width parameters are found to be constant for the three main absorption lines in this range and equal to 0.55 ± 0.05 cm−1. The water vapour-nitrogen line width parameter for the 1.64 mm wavelength line is measured to be 16 per cent. larger than theory having a value of 0.111 ± 0.005 cm−1 and is constant over a range of pressures.
Comparison between theory and observation for the absorption in two submillimetre wave-length windows strongly favours the kinetic equation form of the line shape rather than the more usual Lorentz shape.
Water-vapor absorption lines in the v2 band involving transitions between states of high rotational energy have been found to undergo substantial collisional narrowing in the presence of buffer gases. Measurements were carried out near 5.35 µm, using tunable lead sulfide selenide semiconductor diode lasers.
Applied Physics Letters, published by the American Institute of Physics, features concise, up-to-date reports on significant new findings in applied physics. Emphasizing rapid dissemination of key data and new physical insights, Applied Physics Letters offers prompt publication of new experimental and theoretical papers bearing on applications of physics phenomena to all branches of science, engineering, and modern technology. Content is published online daily, collected into weekly online and printed issues (52 issues per year).
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Measurements of the strengths and air-broadened widths of 223 lines of water vapor have been made with high resolution in the region 2950–3400 cm-1. The strength data of the lines in the 2ν2 and ν1 bands are analyzed to determine the band strengths and the coefficients of the F factors. The band strengths of the 2ν2 and ν1 bands were found to be 1.75±0.08 and 10.3±1.1 cm-2 atm-1 at 296°K, respectively. The selection rules of the lines observed in the ν3 band are forbidden in the symmetric-rotor limit. The majority of the measured strengths of these lines differ from the calculated values because of different asymmetries in the upper and lower vibrational states. Also, Coriolis perturbations in several lines of the ν1 and ν3 bands were observed in the strength measurements. The direct method was applied to determine the air-broadened line widths. The results are compared to the computed values of Benedict and Kaplan. There is good agreement between this work and the computed results for line width values greater than 0.05 cm-1 atm-1. However, for line widths less than 0.05 cm-1 atm-1, the measured values are smaller than the computed widths. A value of 0.018 cm-1 atm-1 is given for the width of the line at 3378.071 cm-1, whereas the calculated value is 0.032 cm-1 atm.
Tunable diode laser measurements of water vapour lines in the 5 μm region have been extended to include oxygen as well as nitrogen broadening. Positive pressure shifts of line positions have been observed for the first time in the v2 band. Absolute calibration of a line position using the CO laser as a reference has also been carried out.
Molecular Physics is a well-established international journal containing original research papers on chemical physics. The journal considers all aspects of the physics and biophysics of molecules, particularly the structure and dynamics of individual molecules and molecular assemblies. The journal also publishes papers on fundamental reaction kinetics and the structure and reactivity of molecules adsorbed on surfaces and at interfaces. Contributions are full papers, preliminary communications, research notes or review articles.
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Russian version (Известия ВУЗов, Радиофизика )
Radiophysics and Quantum Electronics reports on topics such as: radio astronomy; plasma astrophysics; ionospheric, atmospheric and oceanic physics; radiowave propagation; quantum radiophysics; physics of oscillations and waves; physics of plasmas; statistical radiophysics; electrodynamics; vacuum and plasma electronics; acoustics; and solid-state electronics.
Radiophysics and Quantum Electronics is a translation of the peer-reviewed Russian journal Izvestiya VUZ. Radiofizika, published by the Radiophysical Research Institute and N.I. Lobachevsky State University at Nizhnii Novgorod, Russia.
English (Science - Nauka)
A non-linear, least-squares program was used to obtain the line intensities and widths of 91 air-broadened lines in the ν2 rotation-vibration band of water vapor in the region from 1800 to 2100 cm-1. The values obtained for the line intensities are, on the average, about 7% stronger than the Air Force Cambridge Research Laboratories (AFCRL) Atmospheric Absorption Line Parameters Compilation. The experimental values for the half widths of the H2O lines are, on the average, 4% higher than the calculated AFCRL values. The measurements have confirmed the narrow widths of some high J transition lines measured by tunable diode laser spectroscopy.
The Journal of Molecular Spectroscopy presents experimental and theoretical articles on all subjects relevant to molecular spectroscopy and its modern applications. An international medium for the publication of some of the most significant research in the field, the Journal of Molecular Spectroscopy is an invaluable resource for astrophysicists, chemists, physicists, engineers, and others involved in molecular spectroscopy research and practice. Submit your Article online The 'Elsevier Editorial System' (or EES) is a web-based system with full online submission, review and status update capabilities. EES allows you to upload files directly from your computer. This is part of our on-going efforts to improve the efficiency and accuracy of our editorial procedures and the quality and timeliness of the manuscripts published.
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The self-broadening coefficients of 150 lines belonging to the v2 band of H216O between 1770 and 2250 cm-1 have been measured using Fourier transform spectra (resolution ≈ 0.005 cm-1). The four different methods which have been used to deduce the self-broadening coefficients from experiment are described in detail. The estimated average uncertainty is about 15% and varies from 7 to 30%, depending on the method used and on the line involved. Two theoretical calculations, one based on the Anderson-Tsao-Curnutte method and the other on the recent method proposed by Davies, have been performed, retaining only the dipole-dipole interaction. For some lines of the v2 band and for some pure rotation lines, calculations based on other formalisms have also been performed. For all of these calculations, we have used accurate spectroscopic data: precise energy levels, realistic wavefunctions, and a complete dipole-moment operator expansion in order to compute the transition probabilities. As compared to the previously calculated values of the pioneering work of Benedict and Kaplan, where the Anderson-Tsao-Curnutte method was used, our calculations show improvements by about 14% in the agreement between measured and calculated self-broadening coefficients.
Using Fourier transform spectra (resolution ≈ 0.005 cm−1), the self-broadening coefficients of 340 lines belonging to the 2ν2, ν1 and ν3 bands, and to the ν2 + ν3 − ν2 hot band of H216O, have been measured. The average uncertainty is about 19% and varies from 15 to 28% depending on the line involved. The broadening coefficients, by natural water vapor, of 40 other lines belonging to the ν3 and ν1 bands of H217O and H218O have also been measured. Theoretical calculations of self-broadening coefficients are performed, using the Anderson–Tsao–Curnutte method, and taking into account the four intermolecular interactions: dipole–dipole, dipole–quadrupole, quadrupole–dipole, and quadrupole–quadrupole. In these calculations, accurate spectroscopic data have been used: precise energy levels, realistic wavefunctions, and a complete dipole moment operator expansion in order to compute the transition probabilities. Particularly, all resonances between the three interacting vibrational states (020), (100), and (001) have been fully taken into account. For B-type bands, comparisons are made with the self-broadening coefficients previously calculated by Benedict and Kaplan for the pure rotational lines. The Anderson–Tsao–Curnutte method has proved to be very efficient for calculating self-broadening coefficients: the relative differences between observed and calculated values are less than 20% respectively for 68, 79, and 79% of the lines in the 2ν2, ν1, and ν3 bands. These self-broadening coefficients will be useful for the study of the absorption coefficient in line wings.
High-resolution infrared diode laser spectroscopy has been used to determine line strengths, foreign-, and self-broadening coefficients for several transitions in the v2 band of H2O near 6 μm. Sources of systematic experimental error, most notably stray radiation from off-axis modes and thermal etalon effects, were detected and characterized. Their effects on the resulting line parameters were minimized by making appropriate corrections or adjusting experimental conditions such as laser current and temperature. Measured line strengths are found to agree to better than 5% with one published tabulation. Foreign-gas broadening coefficients compare favorably with theoretical values, whereas measured self-broadening coefficients were found to be systematically less.
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The linewidth of the 31.3 ← 22.0 rotational transition of water vapor at 183 GHz has been investigated using a video millimeter wave spectrometer equipped with a signal digitizer. Self- and air-broadening parameters have been obtained for four temperatures over the 299−251°K range; the results are compared with previous experimental and theoretical data.
Measurements of fourteen selected H2O absorption line parameters in the 720-nm region are presented. These results are compared to the most recent and relevant measurements. This paper presents a compilation of absorption cross sections of H2O lines suitable for atmospheric humidity monitoring using an alexandrite laser source as the transmitter.
Pressure-broadening coefficients for several rotation-vibration lines in the ν2 bands of HDO, H216O, and H218O have been determined from laboratory spectra recorded in the 1260- to 1360-cm-1 region with a tunable diode laser spectrometer system. Air and nitrogen were used as the broadening gases and, for all the measured transitions, the nitrogen-broadened half-widths were found to be consistently larger than the corresponding air-broadened half-widths by about 12%. The results have been compared to previously published values when appropriate.
Numerous comparisons between predictions of the model presented in part I of this paper and experimental H2O infrared linewidths are presented. It is shown that our model, contrary to those used up to now, gives accurate results for H2O room-temperature line broadening by O2 and Ar, and for high rotational quantum-number lines by N2. First accurate experimental widths and intensities of some H2O v2-band lines in the 400–900°K temperature range are also presented. Detailed analysis of the data demonstrates the great influence of a "resonance overtaking" mechanism. The latter results from the modifications of both the perturber rovibrational population distribution and kinetic energy with temperature; it strongly enhances the contributions of the collision-induced rotational transitions involving significant energy jumps. This mechanism is well accounted for by our model and quantitatively explains the unusually slow decrease of some linewidths with temperature.
The far-infrared rotational spectrum of H216O has been studied in the spectral range 25–112 cm−1 to measure the foreign-gas collision-broadened linewidths. Measurements of 17 lines broadened by nitrogen and 21 lines broadened by oxygen are reported. The measurements were made at 297°K. From these data, the widths due to air broadening are obtained. The experimental results are compared with recent theoretical calculations and with the case of a constant linewidth, equal to the average experimental width. There is some correlation between the relative experimental linewidths and the theoretical predictions. However, the simple assumption of a constant value for the collision-broadened linewidths gives a better representation for the case of N2- and O2-broadened linewidths than do present detailed theoretical calculations.
JOSA B emphasizes quantum optics, lasers and nonlinear optics. It is the perfect complement to JOSA A. Keywords: Optical physics, Quantum optics, Lasers and nonlinear optics
Pressure broadening and pressure shift in air, nitrogen, oxygen, and argon have been measured for water-vapor lines in the 720-nm wavelength region using a ring dye laser in conjunction with two long path absorption cells. Deviations resulting from the Dicke-narrowing effect were observed between the measured profiles and the standard Voigt profile. The corresponding collision-narrowing coefficients were computed using two Dicke-narrowed profiles, the soft- and the hard-collision profiles. The water-vapor absorption lines broadened by oxygen or argon, where the pressure shifts become comparable to the broadenings, were found to be asymmetric. These asymmetric lines are attributed to statistical dependence or correlation between velocity- and state-changing collisions. A vibrational dependence of the broadening and shifting was observed. Widths and shifts (in magnitude) were found to be significantly smaller for lines associated with upper vibrational states (v′1v′2v′3) = (221) as compared to (v′1v′2v′3) = (301). For each buffer gas under study, a linear relationship between the widths and shifts was measured, the broader lines having the smallest pressure shifts (in magnitude). The average air-to-nitrogen broadening ratio was measured to be 0.907 ± 0.011. We show that the air-broadening coefficient could also be retrieved from the independent measurements of the nitrogen- and oxygen-broadening coefficients. The average line shift in oxygen was found to be twice as large as the shift in nitrogen, indicating that collisions with oxygen molecules contribute significantly to the shift in air. Water-vapor line broadening and shifting in air were investigated in the temperature range from 300 to 400 K. The temperature exponent for air broadening was found to be J-dependent, the broader lines (i.e., low-J lines) having the higher exponents. The average exponent value was measured to be 0.670. The temperature-dependence exponent for the line shift in air was found also to be J-dependent but it showed the opposite behavior (i.e., the high-J lines have the higher exponents). The temperature exponent for line shifting was measured to range between 0.4 and 1.2.
A high-resolution spectrometer incorporating a narrow linewidth tunable dye laser and two long pass absorption cells has been used to provide measurements of water vapor absorption line parameters in the 720-nm wavelength region. Measurements were made of line strengths, self-induced pressure broadenings and shifts, and broadening and shift temperature dependences in the range 300–400 K for 270 water vapor lines between 13 550–13 950 cm-1. Deviations resulting from the Dicke narrowing effect were observed between the measured profiles and the standard Voigt profile. The corresponding collision narrowing coefficients were computed using both the soft and hard collision profiles. Self-induced pressure shift coefficients were found to range between -0.08 and +0.05 cm-1/atm. The temperature dependence exponent for self-broadening was found to be J-dependent with an average value of 0.75 and the average temperature exponent for line-shifting was measured to be 1.57.
About 200 N2-broadening coefficients of H216O lines, absorbing between 9 500 and 11 500 cm-1, have been measured at room temperature with an uncertainty of 7%. These results are compared with previous experimental values and with those appearing in the HITRAN data base.
More than 200 N2-broadening coefficients have been measured at room temperature for H216O lines absorbing between 13 500 and 19 900 cm-1. Also, about 60 additional N2-broadening coefficients have been measured between 10 000 and 11 200 cm-1. The average uncertainty is 8%.
The pressure broadening of the 31,3-22,0 transition of water has been measured over the 80 to 600°K temperature region for O2, N2, and He collision partners. Above 250°K the measurements were made in a conventional equilibrium cell. At lower temperatures a newly developed cell which uses collisional cooling to circumvent the temperature limits ordinarily imposed by vapor pressure was used. For helium broadening and for broadening due to O2 and N2 above 140°K, the results could be fit to the usual exponential temperature dependence with n = 0.49(2), 0.85(3), and 0.74(3), respectively. However, below 140°K the O2 and N2 experimental results are smaller than predicted by this simple exponential relation.
Lorentz air-broadening coefficients and relative intensities have been measured for forty-three lines in the pure rotational band and twenty lines in the v2 band of H216vO between 800 and 1150 cm-11. The results were derived from analysis of nine 0.017-cm-1 resolution atmospheric absorption spectra recorded over horizontal paths of 0.5–1.5 km with the McMath Fourier transform spectrometer and main solar telescope operated on Kitt Peak by the National Solar Observatory. A nonlinear least-squares spectral fitting technique was used in the spectral analysis. The results are compared with previous measurements and calculations. In most cases, the measured pressure-broadening coefficients and intensities are significantly different from the values in the 1986 HITRAN line parameters compilation.
Lorentz nitrogen-broadening coefficients and nitrogen pressure-induced shift coefficients have been measured for six lines in the ν2 band and 98 lines in the ν3 band of H216O. The results were obtained from analysis of 10 high-resolution (0.01 cm−1) infrared absorption spectra recorded at room temperature using the McMath Fourier transform spectrometer of the National Solar Observatory on Kitt Peak. The analysis was performed using a nonlinear least-squares spectrum fitting procedure. The measured nitrogen-broadening coefficients ranged from not, vert, similar 0.04 to not, vert, similar 0.104 cm−1 atm−1, while the nitrogen pressure-induced shift coefficients varied between not, vert, similar+0.004 and not, vert, similar−0.011 cm−1 atm−1. The majority of the measured pressure-induced shift coefficients (>90%) were found to be negative. The results are compared with previous values reported in the literature, where available.
Foreign gas effects by Ar, N2, O2, and air (broadening and frequency shifts) of several rovibrational lines of H2O in the ν2 band were measured precisely by using a stabilized diode laser spectrometer. The additive behavior of the line-broadening parameters is supported by separate measurements with air, oxygen, and nitrogen as foreign gases: the pressure broadening due to air can be calculated from the weighted mean of the measured N2 and O2 coefficients. In contrast, the line shifts are found not to be additive although they respond linearly to pressure increase in the case of a single foreign gas. The line broadening with Ar was found to be much smaller than for N2 or O2. Collisional narrowing phenomena were clearly observed for some of the high-J H2O lines. Line shifts due to Ar are found to be as large as those due to N2 or O2.
The technique of line-locked wavelength modulation with 2ƒ detection is applied to the measurement of water vapor concentration and absorption line parameters by using an 820-nm AlGaAs communications diode laser. Measurements of the 2ƒ signal as a function of the modulation amplitude yield accurate concentrations and line parameters over a pressure range of an order of magnitude and half-widths from 0.02 to 0.15 cm-1. Usingtwo different spectral lines, we determined concentrations and line parameters with 1% precision, and the absolute accuracy of the line parameters is 3% or better. The results have been used to calculate calibration curves for a diode laser humidity monitor.
A tunable diode laser diagnostic based on spectrally resolved laser absorption has been developed to detect water vapor. The system uses a distributed feedback InGaAsP diode laser, emitting at ~ 1.38 µm. The diode laser is tuned in wavelength by modulation of the current, resulting in 1-cm−1 tuning at 80-Hz repetition rate. The directly measured absorption spectra yield values for water-vapor concentration and temperature, as well as a collision-broadening line shape. To our knowledge, we accurately determined required data for H2O line strengths and self-broadening coefficients for several spectral lines in a static cell filled with pure water vapor. The temperature and concentration of the water vapor present in laboratory room air and in the postflame gases above a methane–air flat flame burner have also been measured. These results agree well with calculated values and independent measurements.
A diode laser spectrometer has been used for high accuracy H2O line profile measurements near 5475 cm-1. Measured lineshapes have been least-squares fitted by Voigt profile with a floating Gaussian component. Gaussian component pressure dependence resulting from the Dicke narrowing effect is observed. Line intensities, self- and air-induced broadenings, and shifts of five water vapor lines are presented.
We report water-vapor absorption line measurements that are made by using the first Stokes radiation (930–982 nm) with HWHM 0.015 cm-1 generated by a narrow-linewidth, tunable dye laser. Forty-five absorption line strengths are measured with an uncertainty of 6% and among them are fourteen strong lines that are compared with previous measurements for the assessment of spectral purity of the light source. Thirty air-broadened linewidths are measured with 8% uncertainty at ambient atmospheric pressure with an average of 0.101 cm-1. The lines are selected for the purpose of temperature-sensitive or temperature-insensitive lidar measurements. Results for these line strengths and linewidths are corrected for broadband radiation and finite laser linewidth (0.015 cm-1 HWHM) broadening effects and compared with the high-resolution transmission molecular absorption.
The O2 and N2 pressure-broadening parameters of the 41,4-32,1 rotational transition in the ground vibrational state of H2O have been measured in the temperature range between 100 and 520 K. Above 250 K the measurements were made in an equilibrium cell. Below 250 K a cell, which uses collisional cooling to circumvent the temperature limits imposed by the vapor pressure of the sample gas, was used. The data were fitted to an exponential temperature-dependence for data above 150 K with resultant n values of 0.81(3) for O2 and 0.70(3) for N2, where the entries in parentheses represent the error in the last significant figure of the parameter. Below 150 K the measured pressure-broadening parameters are smaller than those calculated using these values of n.
Pressure effects, broadening and shift, on H20 due to air were measured precisely for 271 rovibrational lines in the ν2 band by using a Fourier transform spectrometer. Rotational dependences of these effects were clearly observed in the present study which includes high-J transitions up to J 18 ← 17. The observed rotational dependence is pronounced. Very small pressure-broadening coefficients were obtained for high-J transitions, e.g., 0.011 cm−1/bar for the unresolved K-doublet, 180,18 ← 171,17 and 181,18 ← 170,17, whereas medium-J transitions exhibit larger broadening, i.e.,74,4 ← 63,3 yields 0.087 cm−1/bar.
Spectrally resolved measurements of pure water vapor absorption spectra have been performed with a tunable diode laser. The laser, a distributed feedback InGaAsP diode, emits in the 1.4-μm region. A total of 12 lines were studied corresponding to rovibrational transitions within the ν1 + ν3 and 2ν1 vibrational bands. A Voigt profile analysis of lineshape is used to infer both intensities and self-collision-broadening coefficients of the water vapor. Good agreement is found between the observed line intensities and those recently measured by Toth. These results are apparently the first published measurements of the broadening coefficient within this spectral range.
The goal of this paper is to discuss a method which allows an accurate determination of the linewidths and the lineshifts from FT spectra recorded at room temperature, by fitting composite profiles and taking into account the phase errors. The results of the measurements of the pressure effects on some CO, H2O, and CO2 lines in the 5-μm spectral region are used to test the method.
Experimental results on the collisional self-shift and self-broadening of the 643-550 rotational water line at 439 GHz are presented in the temperature range 250-390 K. The (T0/T) exponent for the shift and broadening are α = 2.59(20) and β = 0.62(9), respectively. A method for the remote measurement of gas temperature, based on spectral collisional shift and broadening, is proposed.
The time-resolved quasi-cw form of intracavity laser spectroscopy is used for the quantitative determination of absolute intensities and self-broadening coefficients of weak vibration-rotation lines of water that absorb in the region of the 720-nm band. The studies have been conducted using a 0.68-m-long intracavity absorption cell, and the data are analyzed both by directly fitting the absorption lineshape and by the curve of growth method. Values determined for some of the stronger lines are compared with the ones obtained in previous studies where multipass absorption cells and alternative instrumental techniques were employed. The comparisons show that the accuracy of the intracavity laser spectroscopy technique is comparable to that obtained by the use of other techniques. In addition, intensities and pressure-broadening parameters of several previously unanalyzed transitions are reported.
Measurements of CO2-broadened half-widths of 31 transitions belonging to the ν1, 2ν2, and ν3 bands of water vapor were made at T = 294.4 K. Calculations following the formalism of Robert and Bonamy with an electrostatic and atom-atom interaction potential and dynamics correct to second order in time were performed for 562 transitions relevant to the 1- to 2.5-μm region. The calculations were compared with the measurements made in this work, a recent study by Langlois et al. (J. Mol. Spectrosc.167, 272-281, 1994), and an earlier work by Varanasi et al. (J. Quant. Spectrosc. Radiat. Transfer.11, 223-230, 1971). The calculations compared with experiment show average percent differences of +12, +1.5, and −8, respectively, for the works listed above. Unfortunately there are no common lines measured by the different groups so a direct comparison of the measurements is not possible. Calculations of the temperature dependence of the halfwidths were made for 34 transitions. The temperature dependence of the half-widths determined from theory and the measurements of Langlois et al. agree reasonably well with two exceptions.
Measurements of line broadening and lineshifts induced by collisions with He, Ne, Ar, Kr, and Xe for absorption lines of the ν1 + 3ν3 band of H2O and the ν1 and ν3 bands of SO2 were performed by applying laser photoacoustic and diode laser spectroscopy. A modified version of the Anderson-Tsao-Curnutte theory, neglecting Anderson′s interrupting, was employed for the description of the collisional half-width and shift behavior of the spectral lines in the case of dipole molecule interactions with noble gas atoms. The comparison of the experimental and calculated data shows that the derived formulae describe precisely the behavior of broadening and shift coefficients and their dependence on the polarizabilities of the perturbing atoms and of the absorbing molecule.
Microwave measurements of pressure shifts by mixtures of gases are reported. Recently in IR measurements a nonlinear dependence of shift vs concentration was found (J. Mor. Spectrosc.153, 406-418, (1992). Our measurements were carried out on the 110 ← 101 water (H216O) line near 556 GHz using nitrogen, oxygen, and their mixtures as perturbers. The result showed no measurable nonlinearity. Further experiments are discussed.
Absolute absorption rates of mixtures of water vapor and carbon dioxide have been measured at 239 GHz which is in an atmospheric window for the rotational and vibrational spectra of both species. The dependence on pressure as well as temperature has been obtained. The experimental data are compared with models using conventional lineshapes. As these models require the knowledge of the collisional linewidths of the H2O broadened by CO2, theoretical calculations using the Robert–Bonamy formalism have been carried out. A very large “continuum effect” is observed when comparing the experimental absorption with the models, as well for the magnitude of the absorption discrepancy and for the strong temperature dependence of this absorption. Collision induced absorption (CIA) has also been measured at this frequency. These results can be applied to planetary observations.
To support the remote sensing of the outer planets, absorption spectra of H2O broadened by H2 were recorded at room temperature using two Fourier transform spectrometers. The data from 1260 to 2070 cm−1 and 3420 to 4045 cm−1 were obtained at 0.0056 and 0.012 cm−1 resolution (unapodized), respectively, with the McMath FTS located at Kitt Peak National Observatory/National Solar Observatory. The remainder of the spectral data from 55 to 328 cm−1 was taken at 0.0056 cm−1 with the HR120 Bruker FTS at the Jet Propulsion Laboratory. Some 630 H2-broadened linewidths of H216O were obtained with precisions of 2–7% for the four strongest water bands: rotational at 0 cm−1; v2 at 1595 cm−1; v1 at 3657 cm−1 and v3 at 3756 cm−1. The intensity of the weakest measured transition was 0.0065 cm−2/atm at room temperature. Within a band, the widths varied from 0.101 to 0.033 cm −1/atm at room temperature for 0 ≤ J ≤ 12 and 0 ≤ Ka ≤, 6. Systematic patterns were detected in the widths as a function of ΔJ, J, Ka, and asymmetry. At low Ka, the widths decreased with increasing J, but for Ka> 2, the widths generally increased with increasing J. Examination of the vibrational dependencies of the three perpendicular bands also revealed that the widths of the v2 and rotational transitions were nearly the same (within 3%), but the widths of v1 were generally larger (up to 18%). The limited width measurements reported by others in the pure rotational and 1.4 μm regions supported the conclusions concerning vibrational dependencies.
Measurements of CO2-broadened line shifts of 29 transitions belonging to the v1, 2v2 and v3 bands of water vapor are made at T = 294.4 K. The halfwidths of 31 transitions were previously reported [R. R. Gamache et al (1995)]. Calculations of the halfwidth and line shifts based on a fully complex implementation of the formalism of Robert and Bonamy are made for these transitions. The calculations employ an electrostatic, Lennard-Jones (6–12) atom-atom, and isotropic induction and dispersion components of the potential and dynamics correct to second order in time. The results are compared with the measured values and very good agreement is observed for both halfwidths and line shifts. A new feature in this approach is that the real and imaginary components of the S matrix affect both the halfwidth and the line shift. It is shown here that the imaginary parts of the S matrix strongly affect the calculated H2O-CO2 halfwidths.
