The collision-induced absorption of gaseous CO2is the primary source of far-infrared opacity of the atmosphere of Venus. At the temperatures and densities of the venusian atmosphere, the absorption is due mainly to binary collisions of CO2molecules. Using a realistic anisotropic intermolecular potential and assuming the absorbing dipole to be due to the electrostatic induction and a quantum overlap, a series of molecular dynamics simulations were performed for the temperature range 200 to 800 K, and the roto-translational collision-induced absorption spectra at frequencies from 0 to 250 cm−1were derived. The absorption coefficient in the submillimeter region, used in constituency retrieval 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−1was found to be almost 10 times higher than at 200 K. Earlier works relied on experimental RT CIA data at a fixed temperature of 300 K. The new, temperature-dependent absorption bands may, when included in the analysis of the atmospheric radiative transfer of the planet, help explain the observed high far-infrared opacity of the lower layers of the atmosphere. To make the results of the simulations readily available for atmospheric abundance and radiative transfer analysis, an analytic model of the roto-translational collision-induced absorption spectral profile, applicable from 200 to 800 K, is being proposed here. The FORTRAN computer code of this newly developed model is available from the authors on request.
ICARUS is the official publication of the Division for Planetary Sciences of the American Astronomical Society and is dedicated to reporting the results of new research - observational, experimental, or theoretical - concerning the astronomy, geology, meteorology, physics, chemistry, biology, and other scientific aspects of our Solar System or extrasolar systems.
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Comparison between measured and modeled RT CIA spectra by our BCBC model. The experimental results are from Ho et al. (1971) and Dagg (private communication).
