A semiclassical theory of the width and shift of isolated infrared and Raman lines in the gas phase is developed within the impact approximation. A parabolic trajectory model determined by the isotropic part of the interaction potential allows a satisfactory treatment to be made of the close collisions leading to an analytical expression for the elastic collision cross section. A numerical test of this theory has been made for HCl-Ar by comparing the present results to those of previous infinite order treatments using numerical curved classical trajectories. Extension to the diatom-diatom collisions is then made by expressing the anisotropic potential using an atom-atom interaction model which takes both the long and short range contributions into account. Numerical applications have been performed for the Raman line widths of pure N2, CO2 and CO and for the infrared line widths of pure CO and of CO perturbed by N2 and CO2. A good quantitative agreement with experiments is obtained for all the considered cases and a correct variation of the broadening coefficient with the rotational quantum number is achieved in opposition to the previous results. A consistent variation of the line broadening with temperature is also obtained even for high rotational levels.

https://hal.archives-ouvertes.fr/jpa-00209180/document

Short range force effects in semiclassical molecular line broadening calculations

The Mars Climate Sounder (MCS) onboard the Mars Reconnaissance Orbiter is the latest of a series of investigations devoted to improving the understanding of current Martian climate. MCS is a nine-channel passive midinfrared and far-infrared filter radiometer designed to measure thermal emission in limb and on-planet geometries from which vertical profiles of atmospheric temperature, water vapor, dust, and condensates can be retrieved. Here we describe the algorithm that is used to retrieve atmospheric profiles from MCS limb measurements for delivery to the Planetary Data System. The algorithm is based on a modified Chahine method and uses a fast radiative transfer scheme based on the Curtis-Godson approximation. It retrieves pressure and vertical profiles of atmospheric temperature, dust opacity, and water ice opacity. Water vapor retrievals involve a different approach and will be reported separately. Pressure can be retrieved to a precision of 1–2% and is used to establish the vertical coordinate. Temperature profiles are retrieved over a range from 5–10 to 80–90 km altitude with a typical altitude resolution of 4–6 km and a precision between 0.5 and 2 K over most of this altitude range. Dust and water ice opacity profiles also achieve vertical resolutions of about 5 km and typically have precisions of 10^(−4)–10^(−5) km^(−1) at 463 cm^(−1) and 843 cm^(−1), respectively. Examples of temperature profiles as well as dust and water ice opacity profiles from the first year of the MCS mission are presented, and atmospheric features observed during periods employing different MCS operational modes are described. An intercomparison with historical temperature measurements from the Mars Global Surveyor mission shows good agreement.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009JE003358

Mars Climate Sounder limb profile retrieval of atmospheric temperature, pressure, and dust and water ice opacity

A simple parameterization of infrared cooling between altitudes of 30 and 70 km consists of the sum of the exact cooling for a reference temperature profile and a Newtonian cooling approximation for departures from this profile. The parameterization is developed by using the 1962 standard atmosphere for the reference temperature. The exact line-by-line calculation of cooling gives total infrared cooling rates that in the vicinity of the stratopause are somewhat greater (∼1 deg day−1) than the values obtained by previous investigators, apparently because the present study includes ‘second hot bands’.

Method of parameterization for infrared cooling between altitudes of 30 and 70 kilometers

Water-vapor line broadening and shifting by air, nitrogen, oxygen, and argon in the 720-nm wavelength region

A transmittance model was developed for the 200-2000/cm region for interpretation of high spectral resolution measurements of laboratory absorption and of planetary thermal emission. The high spectral resolution requires transmittances to be computed monochromatically by summing the contribution of individual molecular absorption lines. A magnetic tape atlas of H2O,O3, and CO2 molecular line parameters serves as input to the transmittance model with simple empirical representations used for continuum regions wherever suitable laboratory data exist. The theoretical formulation of the transmittance model and the computational procedures used for the evaluation of the transmittances are discussed. Application is demonstrated of the model to several homogenous path laboratory absorption examples.

/pdf/direct-integration-transmittance-model-195ru02a75.pdf

Direct integration transmittance model

Anderson's theory on the non-adiabatic collision broadening of the infrared spectral lines has been applied to CO2-CO2 and CO2-N2 collisions. The intermolecular attractive force assumed in this study is that due to either CO2 quadrupole-CO2 quadrupole interaction or CO2 quadrupole-N2 quadrupole interaction. The self-and N2-broadened line widths are calculated on four important bands in the 15μ and 4·3 μ band regions, assuming several different values for the CO2 and N2 quadrupole moments and taking into account the Maxwell-Boltzmann distribution law of the colliding velocity. The results are then used for the determination of plausible values of CO2 and N2 quadrupole moments by comparing with available experimental results.

Estimation of rotational line widths of carbon dioxide bands

The Anderson-Tsao-Curnutte's theory (1.2) of collision broadening has been applied to the asymmetric-top molecules. Theoretical formulations of broadening due to dipole-dipole, dipole-quadrupole, quadrupole-dipole, quadrupole-quadrupole and Debye induction force interactions are developed. Asymmetry of the electric charge distribution was taken into account in considering the quadrupole moment of the asymmetric-top molecule. It is shown that the shape of the electric-charge distribution affects the value of the line width when the quadrupole moment is large.

T. Aoki

Papers

Estimation of rotational line widths of carbon dioxide bands

Line broadening theory of asymmetric-top molecule