Cover Page/Proposal Summary

ROSS-99    NRA 99-OSS-01

Date Due: 5/3/99

Interpretation of planetary observations and modeling of planetary atmospheres are dependent on accurate laboratory data for the properties and processes of various atmospheric constituents. It is important that these data be taken over the appropriate range of parameters, e.g., temperature and composition; however, temperature-dependent laboratory data for most properties or processes of relevant species are particularly meager. This proposal addresses the needs of the planetary atmospheres community for temperature-dependent molecular relaxation rates which serve as input for thermal-structure models of planetary atmospheres. In the absence of low-temperature measurements, modelers must extrapolate high-temperature data to the temperatures of interest. These extrapolations can cover large temperature ranges, thus introducing significant errors in the models. We propose to measure relaxation rates for several light hydrocarbons at temperatures appropriate for the outer planets and their satellites (90 to 300 K). Temperature-dependent vibrational-to-translational relaxation of methane by helium, argon, normal and ortho/para hydrogen, and nitrogen will be determined using a photoacoustic apparatus specifically constructed for these experiements, and similar data will then be acquired for acetylene. A pump-probe technique will be implemented to measure vibrational-to-translational rates for larger hydrocarbons as well as vibrational-to-vibrational or vibrational-to-rotational transfer rates for both small and large hydrocarbons. Results from these experiments will be of immediate use in atmospheric models constructed to guide the engineering development of, planning for, and interpretation of data from a variety of planetary missions: the Kuiper/Pluto Express, Cassini/Huygens, and the Galileo Orbiter/Probe.