Line coupling in the temperature and frequency dependences of absorption in the microwindows of the 4.3 μm CO2 band

Abstract The shapes of the self- and N2-broadened ν3CO2 fundamental vibration-rotation band in the microwindows (troughs between the lines) have been measured at various temperatures. Important deviations with respect to the superposition of Lorentzian profiles are observed. These deviations are interpreted in terms of line coupling, which redistributes the intensity in the whole band. In order to take into account this line coupling, two models are considered within the frame of the impact theory. The first model uses the strong-collision approximation to describe the rotational energy transferred by collisions. It leads to a simple analytical expression for the band profile. The second model is based on the exponential-gap law. These two models account well for the frequency dependence of the measured absorption in the microwindows and for the temperature dependence in the case of the N2-broadened CO2 band but not in the self-broadened case. The influence of the line-coupling rotational distribution, which differs significantly in the two models, is discussed. The possible role of the finite duration of collision in rotational energy transfer is examined.

[1]  Sunil Sarangi,et al.  Line shape parameters for HCl and HF in a CO2 atmosphere , 1972 .

[2]  S. Barton,et al.  A polynomial energy-gap model for molecular linewidths , 1985 .

[3]  C. Boulet,et al.  Towards the calculation of line mixing effects: a semiclassical calculation of rotationally inelastic cross sections , 1985 .

[4]  R. Mcclung.  On the extended rotational diffusion models for molecular reorientation in fluids , 1977 .

[5]  D. C. Robertson,et al.  Measured and predicted atmospheric transmission in the 4.0-5.3-microm region, and the contribution of continuum absorption CO(2) and N(2). , 1979, Applied optics.

[6]  P. Rosenkranz.  Shape of the 5 mm oxygen band in the atmosphere , 1975 .

[7]  A. Eckbreth,et al.  Pressure-induced narrowing of the cars spectrum of N2☆ , 1980 .

[8]  R. Le Doucen,et al.  Temperature dependence of the absorption in the region beyond the 4.3-Mum band head of CO2. 1: Pure CO2 case. , 1985, Applied optics.

[9]  E. Arie,et al.  Spectroscopie par Source Laser. I. Etude Expérimentale des Intensités et Largeurs des Raies de la Transition 0001–(1000,0200)I de CO2 , 1972 .

[10]  Sheldon Green,et al.  ON THE USE OF PRESSURE BROADENING DATA TO ASSESS THE ACCURACY OF CO-He INTERACTION POTENTIALS - eScholarship , 1980 .

[11]  A. R. Edmonds.  Angular Momentum in Quantum Mechanics , 1957 .

[12]  Ian R. McDonald,et al.  Interaction site models for carbon dioxide , 1981 .

[13]  R. Nordstrom,et al.  The N2-broadened water vapor absorption line shape and infrared continuum absorption. I - Theoretical development. II - Implementation of the line shape , 1982 .

[14]  R. Shafer,et al.  Quantum scattering theory of rotational relaxation and spectral line shapes in H2–He gas mixtures , 1973 .

[15]  G. Millot,et al.  Rotational collisional line broadening at high temperatures in the N2 fundamental Q-branch studied with stimulated Raman spectroscopy , 1986 .

[16]  N. N. Filippov,et al.  Influence of line interference on the vibration-rotation band shapes , 1984 .

[17]  K. Lam.  Application of pressure broadening theory to the calculation of atmospheric oxygen and water vapor microwave absorption , 1977 .

[18]  P. Rosenkranz.  Comment on ‘‘Absorption and dispersion in the O2 microwave spectrum at atmospheric pressures’’ , 1982 .

[19]  R. J. Hall,et al.  Application of the rotational diffusion model to gaseous N2 CARS spectra , 1982 .

[20]  Earl W. Smith.  Absorption and dispersion in the O2 microwave spectrum at atmospheric pressures , 1981 .

[21]  A. Burshtein,et al.  On the shape of the Q-branch of Raman scattering spectra in dense media. Theory , 1979 .

[22]  V. Malathy Devi,et al.  Diode laser measurements of strengths, half-widths, and temperature dependence of half-widths for CO2 spectral lines near 4.2 μm , 1984 .

[23]  G. C. Tabisz,et al.  Motional narrowing of Raman Q branches of linear molecules , 1982 .

[24]  Michael E. Thomas,et al.  The N2-broadened water vapor absorption line shape and infrared continuum absorption—II. Implementation of the line shape☆ , 1982 .

[25]  G. J. Rosasco,et al.  Line interference effects in the vibrational Q-branch spectra of N2 and CO , 1983 .

[26]  Michael L. Klein,et al.  Pairwise additive effective potentials for nitrogen , 1980 .

[27]  George Birnbaum,et al.  The shape of collision broadened lines from resonance to the far wings , 1979 .

[28]  A. Ben-Reuven.  Impact Broadening of Microwave Spectra , 1966 .

[29]  R. Gordon.  On the Rotational Diffusion of Molecules , 1966 .

[30]  G. J. Rosasco,et al.  Rotational collisional narrowing in the NO fundamental Q branch, studied with CW stimulated Raman spectroscopy , 1984 .

[31]  S. D. Tvorogov,et al.  Formation of the Far Wings Contour of Spectral Lines Broadened by a Foreign Gas; Analysis of Exponential Decrease of Continuous Absorption Beyond the Band Head of the 4.3-micro Band of CO(2). , 1973, Applied optics.

[32]  C. Boulet,et al.  A theoretical and experimental study of the infrared line shape from resonance to the wings for uncoupled lines , 1985 .

[33]  S. Green.  On the amount of information in rotational relaxation experiments with application to microwave transient T1 and T2 rates , 1978 .

[34]  C. Boulet,et al.  Temperature dependence of the absorption in the region beyond the 4.3-microm band head of CO(2) . 2: N(2) and O(2) broadening. , 1985, Applied optics.

[35]  R. Gordon,et al.  Correlation Functions for Molecular Motion , 1968 .

[36]  R. Armstrong.  Moment analysis of a model correlation function , 1982 .