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Accurate measurements of collision-induced absorption by [O.sub.2] and [O.sub.2]-[N.sub.2] mixtures in the fundamental band near 6.4 [[micro]meter] have been made. A Fourier-transform spectrometer was used with a resolution of 0.5 [cm.sup.-1]. Absorption has been investigated in the 0-20-atm and 193-293 K pressure and temperature ranges, respectively. The current measurements confirm that the broad [O.sub.2] continuum carries small features whose attribution is not yet clear. Available experimental data in the 190-360 K temperature range have been used to build a simple, low cost computer, empirical model that is well adapted for computation of atmospheric [O.sub.2] absorption. Tests show that it is accurate, contrary to predictions of widely used atmospheric transmission codes. Key words: Oxygen, collision-induced absorption, infrared.

Measurements of pure C[O.sub.2] absorption in the 2.3-[[micro]meter] region are presented. The 3800-4700-[cm.sup.-1] range has been investigated at room temperature for pressures in the 10-50-atm range by using long optical paths. Phenomena that contribute to absorption are listed and analyzed, including the contribution of far line wings as well as those of the central region of both allowed and collision-induced absorption bands. The presence of simultaneous transitions is also discussed. Simple and practical approaches are proposed for the modeling of absorption, which include a line-shape correction factor [Chi] that extends to approximately 600 [cm.sup.-1] from line centers. Key words: C[O.sub.2] infrared spectra, induced band, far wings.

The collision-induced absorption fundamental band of N2 has been investigated in the 2100-2600 cm to the -1 spectral region. Laboratory measurements have been undertaken over the temperature range 193-297 K. Binary-absorption coefficients for N2 absorption induced by collisions with N2 and O2 are reported and compared with N2 temperature-dependent continua from atmospheric measurements.

The energy corrected sudden approach is used in order to deduce collisional parameters and to model infrared quantities in Π←Σ bands of CO[SUB2]-He and CO[SUB2]-Ar mixtures in the 200-300 K temperature range. Measured line-broadening coefficients and absorption in the Q-branch of the v[SUB2] band at moderate pressure are first used for the determination (from a fit) of the time constant associated with the relaxation of the second order traceless tensor of the rotational angular momentum (all other collisional quantities have been determined previously). The results obtained are consistent with previous (calculated) temperature dependent values of the depolarized Rayleigh cross sections. The model is then successfully tested through computations of absorption in the v[SUB2] and (v[SUB1] + v[SUB2])[SUBI] bands at elevated densities. Analysis of line-mixing effects is made, including study of the influence of interbranch transfers and of Coriolis coupling. Differences between the effects of collisions with He and Ar are pointed out and explained. [ABSTRACT FROM AUTHOR]

Presents the experimental and theoretical results on the influence of line mixing on the shape of infrared carbon dioxide branches. Importance of the findings for atmospheric applications; Study of Q branches of the symmetry for many conditions of temperature, total pressure and mixture; Theoretical approach based on the Energy Corrected Sudden approximation.

Line coupling induced by collisions leads to drastic modifications of the spectral profile of the 0003–0000 of CO2 pressurized by helium. Calculation of these modifications have been performed by using two recent energy corrected sudden (ECS) formalisms. The two formulations lead to theoretical predictions rather similar and in good agreement with the available data over extended ranges of frequency and perturber pressure. It has been shown that a simultaneous fit of the pressure broadened linewidths and the near wing profile allows a more accurate determination of the basic ECS parameters. For that purpose, it has been necessary to extend the measurement of the broadened widths to high J values (up to J≊90). [ABSTRACT FROM AUTHOR]

Here we present the first line-by-line measurements of interference parameters Y0k describing line-mixing effects in the weak overlapping regime for He-broadened CO lines in the 0–1 and 0–2 bands at 296 K. A detailed analysis of the line shape at intermediate perturber pressures (up to about 10 atm) has been performed, starting from previous theoretical calculations, which has demonstrated the possibility of an individual measurement of Yk parameters. The method is based on the existence of a component of the line shift, quadratic with the perturber pressure (density) and proportional to Y0k. Comparison of our measurements with results predicted from coupled-states calculations shows good overall agreement. Linear pressure shifts have also been simultaneously measured. The uncertainty on the data is important since linear shifts are very small; however, some features can be considered as significant although we have no clear understanding of them. Possible explanations are discussed. [ABSTRACT FROM AUTHOR]

Self-broadened and N2, Ar, He-broadened halfwidth and pressure shift coefficients of the rotational transitions in the 0003–0000 band of 12C16O2 have been measured from laboratory absorption recorded at room temperature with a Fourier transform spectrometer. Comparison is made with the results of a theoretical calculation based on a semiclassical model. Good agreement is obtained for all the IR vibrational bands for which data are available. It has been shown that the shifts mainly originate from vibrational dephasing. Infrared line shifts have been compared with results obtained from stimulated Raman spectroscopy and we show that they are not consistent. A number of possible explanations have been discussed to account for this discrepancy. [ABSTRACT FROM AUTHOR]

The absorption beyond the ν3-band head of CO2 broadened by argon has been measured at room temperature. The absorption exhibits a strong sub-Lorentzian behavior (several orders of magnitude) resulting from collisionally induced line interferences which transfer intensity from this wing region to the ν3-band center. This wing absorption region implies detuning frequencies from resonances much larger than the reciprocal duration of collision. Consequently, finite duration of collisions in rotational energy transfers and initial correlations must be included in absorption calculation. A line-by-line coupling theory accounting for both these effects has been recently proposed [J. Chem. Phys. 89, 625 (1988)] and is applied here to a detailed study of the CO2–Ar collisional system. A convenient generalized detailed balance correction is introduced in this theory to overcome the limitation of the assumed resonant character of the energy transfer in the short time limit with respect to the thermal time ( βh)-1. The calculated absorption is in quantitative agreement with experiment. The origin and the nature of the empirical correcting factor currently used in similar studies are clearly established on a firm physical basis. [ABSTRACT FROM AUTHOR]