ROTO-TRANSLATIONAL COLLISION-INDUCED ABSORPTION OF CO2 FOR THE ATMOSPHERE OF VENUS AT FREQUENCIES FROM 0 TO 250 CM(-1), AT TEMPERATURES FROM 200 TO 800 K

The collision-induced absorption of gaseous CO2 is the primary source of far-infrared opacity of the atmosphere of Venus. At the temperature s and densities of the venusian atmosphere, the absorption is due main ly to binary collisions of CO2 molecules. Using a realistic anisotropi c intermolecular potential and assuming the absorbing dipole to be due to the electrostatic induction and a quantum overlap, a series of mol ecular dynamics simulations were performed for the temperature range 2 00 to 800 K, and the roto-translational collision-induced absorption s pectra at frequencies from 0 to 250 cm(-1) were derived. The absorptio n coefficient in the submillimeter region, used in constituency retrie val studies, decreases more than 10 times in the temperature range 200 to 800 K. On the other hand, the absorption coefficient at 800 K and at the frequency range above 150 cm(-1) was found to be almost 10 time s higher than at 200 K. Earlier works relied on experimental RT CLA da ta at a fixed temperature of 300 K. The new, temperature-dependent abs orption bands may, when included in the analysis of the atmospheric ra diative transfer of the planet, help explain the observed high far-inf rared opacity of the lower layers of the atmosphere. To make the resul ts of the simulations readily available for atmospheric abundance and radiative transfer analysis, an analytic model of the roto-translation al collision-induced absorption spectral profile, applicable from 200 to 800 K, is being proposed here. The FORTRAN computer code of this ne wly developed model is available from the authors on request. (C) 1997 Academic Press.