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B.P. Michael (CUA and NASA/GSFC), J.E. Allen, Jr. (NASA/GSFC)
Both the interpretation of planetary observations and modeling of planetary atmospheres are dependent on accurate data for the properties and processes of various atmospheric constituents. Such information can also be critically important for mission planning, e.g., Pluto-Kuiper Express, and/or in-flight corrections, e.g., Cassini/Huygens. As an example, temperature-dependent rates for relaxation of methane by nitrogen, most notably vibrational-to-translational (V-T) energy transfer, are required for the planning and execution of these two missions. However, there are very little experimental data available on the interaction of these two molecules, thus necessitating the use of theoretical or empirical methods to determine the desired information. Unfortunately, these methods can sometimes lead to large errors in the required data that can in turn affect the interpretation of both observation and modeling results. Here we assess several methods for determining the temperature dependence of the V-T rates for the methane-nitrogen system by comparing the predictions of these methods with existing experimental data for the interaction of methane with several monoatomic collision partners (helium, neon, and argon).