The collisions between two oxygen molecules give rise to O4 absorption in the Earth atmosphere. O4 absorption is relevant to atmospheric transmission and Earth’s radiation budget. O4 is further used as a reference gas in Differential Optical Absorption Spectroscopy (DOAS) applications to infer properties of clouds and aerosols. The O4 absorption cross section spectrum of bands centered at 343, 360, 380, 446, 477, 532, 577 and 630 nm is investigated in dry air and oxygen as a function of temperature (203–295°K), and at 820 mbar pressure. We characterize the temperature dependent O4 line shape and provide high precision O4 absorption cross section reference spectra that are suitable for atmospheric O4 measurements. The peak absorption cross-section is found to increase at lower temperatures due to a corresponding narrowing of the spectral band width, while the integrated cross-section remains constant (within o3%, the uncertainty of our measurements). The enthalpy of formation is determined to be ΔH250 = -0.12±0.12 kJ mol-1, which is essentially zero, and supports previous assignments of O4 as collision induced absorption (CIA). At 203°K, van der Waals complexes (O2-dimer) contribute less than 0.14% to the O4 absorption in air. We conclude that O2-dimer is not observable in the Earth atmosphere, and as a consequence the atmospheric O4 distribution is for all practical means and purposes independent of temperature, and can be predicted with an accuracy of better than 10-3 from knowledge of the oxygen concentration profile.
The infrared fundamental band and the five strongest near-infrared and visible electronic bands of gaseous oxygen were studied from 90 to 115 K with path lengths up to 140 m in two low-temperature multiple-traversal absorption cells. The profile of the fundamental band is in good agreement with the theory of quadrupole-induced absorption except for a low-intensity residual in the Q-branch region. Although the electronic bands are less amenable to complete analysis, the general validity of a Boltzmann relation in their intensity distributions confirms their collision-induced nature. The temperature variation of the integrated band intensities is indicative of quadrupole induction for the fundamental and of overlap induction for the electronic bands; a somewhat too sharp rise at low temperatures may be due to the neglect of the quadrupole–quadrupole coupling in evaluating the pair distribution function.
Absorption spectra of gas-phase molecular oxygen and zero air at temperatures of 223 and 283 K have been measured in the laboratory using a coolable multipass-optics gas cell and Fourier transform spectroscopy in the wavelength range 455 to 830 nm (12,000–22,000 cm−1). Net absorption cross sections of the O2A−, B−, and γ-bands at <0.002 nm spectral resolution, and pressures of 100 and 1000 hPa zero air have been determined. Binary absorption cross sections of the collision-induced O4 bands at <0.18 nm spectral resolution and a pressure of 1000 hPa pure oxygen have been determined, with corrections for the O2 γ-band absorption. Calculated integrated absorption intensities and, for the O2A− and B−bands, “effective” Einstein A-coefficients are compared with previous literature values.
The absorption spectrum of O2 and O2‐O2 collision pairs were measured over the wavelength range from 330 to 1140 nm using pressures of O2 from 1 to 55 atm at 298 K. Absorption cross sections, pressure dependences, band centers, and full widths at half maximum of the observed absorption bands centered at 343.4, 360.5, 380.2, 446.7, 477.3, 532.2, 577.2, 630.0, 688, 762, and 1065.2 nm are reported. The absorption bands centered at 360.5, 380.2, and 477.3 nm were also measured at 196 K and their temperature dependences were characterized.
The first atmospheric profiles of the ultraviolet/visible (UV/vis) absorption bands of the collision complex O2-O2, or O4 in brief, are reported. The O4 absorption profiles are inferred from direct Sun spectra observed from the LPMA/DOAS (Laboratoire Physique Mol•culaire et Application/Differential Optical Absorption Spectroscopy) balloon gondola. Seven 04 absorption bands - centered at ~360.7, 380.2, 446.7, 477.1, 532.2, 577.2, and 630.0 nm - are investigated for atmospheric pressures (p) ranging from ~500 hPa to ~40 hPa and temperatures (T) ranging from 203 K to 250 K. For the encountered atmospheric condi- tions, it is found that, (a) the band shapes do not change with T and p and (b) the peak collision pair absorption intensities (c•i) concurrently increase with decreasing T (by about 11% over a AT--50 K). That result is in agreement with previous laboratory O4 studies mostly conducted at high O2 partial pressures (up to several hundred bars). Furthermore, by reasonably assuming that the 04 absorption cross sections are T-independent, the inferred Tdependence of ozi(T) suggests a thermally averaged enthalpy change < AH > ---(1207+83) J/Mol involved in the formation of O4. Our inferred AH is in reasonable agreement with the orientation and spin averaged 04 well depth De(O4) (= -(1130+80) J/Mol) measured in a recent O2-O2 collision experiment, when accounting for the rovibrational energy change during O4 formation (186 J/Mol).
Two collision-induced absorption features of oxygen have been investigated by means of the laser-based cavity ring-down technique at pressures between 0 and 1000 hPa and at temperatures in the range 184–294 K. Peak cross sections, resonance widths and integrated cross sections, as well as spectral profiles, have been determined for the broad O2O2–O2O2 resonances centered at 477 and 577 nm. Results are compared with previous measurements to establish an updated temperature dependence for the cross sections of both resonances, yielding integrated cross sections, that exhibit a minimum near 200 K and that increase in a near-linear fashion in the atmospherically relevant range of 200–300 K. A significant increase in the widths of the resonance profiles upon temperature increase is firmly established. Parameters and temperature-dependent trends for the shape and strengths of the resonances are produced, that can be implemented in cloud retrieval in atmospheric Earth observation.
Atmospheric observations of the O4 absorption bands at 360.5, 380.2, 477.3, 532.2, 577.2 and 630.0 nm are presented for different atmospheric conditions (clear and cloudy skies) and viewing geometries (direct and zenith-scattered light observations). From the observations of direct moonlight it was possible to derive absolute O4 absorption cross sections for atmospheric conditions. We found that the relative shape of the observed absorption bands is similar to those of the O4 spectrum measured by Greenblatt et al.  in the laboratory. However, in general (except for the absorption band at 380.2 nm), the O4 absorption cross sections derived in this study are larger by several percent compared to those of the other (mainly laboratory) observations. Using the observations of zenith-scattered light, we investigated the radiative transport through the atmosphere. Our observations under cloudy sky conditions confirmed that the light path enhancement due to multiple Mie scattering on cloud droplets is independent of wavelength. From the observations under clear-sky conditions we studied the influence of Mie scattering on aerosol. It was not possible to describe the selected clear-sky measurements by taking into account only Rayleigh scattering. We found that the comparison of the O4 measurements with model results for different sets of assumed aerosol extinctions provides a new, very sensitive tool to derive aerosol parameters from zenith sky ground-based measurements.