Cover Page/Proposal Summary

ROSS-00    NRA 00-OSS-01

Date Due: 4/28/2000

We propose laboratory measurements of the submillimeter spectra of gases and gas mixtures at low temperatures. The experiments are designed to detect weak spectral features due to van der Waals pairs of molecules, or dimers, which form at low temperatures. These spectra are necessary to properly interpret new low frequency measurements (10--600 1/cm) of the atmospheres of Titan and Saturn which will be obtained by the Composite Infrared Spectrometer (CIRS) on the Cassini spacecraft. The gases to be studied are nitrogen, and mixtures of nitrogen with argon, methane and hydrogen as they pertain to potential features found in Titan's spectrum; and hydrogen, and mixtures of hydrogen with methane, argon and nitrogen as these dimers may be observed in the spectrum of Saturn. Although H2 and He do not form bound pairs, the enhancement of the H2 collision-induced spectrum by helium will also be studied. The work will use a unique differential Michelson interferometer and absorption cell system specifically designed to observe weak absorptions over the frequency region 2--100 1/cm. Experiments will be conducted using conditions of pressure and temperature very near to those found in Titan's and Saturn's atmospheres. The submillimeter region is of particular interest as dimer bound state transitions occur here, and with the exception of N2 and N2-Ar, no low temperature laboratory measurements have been conducted of these dimer systems below 1/20 cm. The work bears directly on the argon abundance of Titan, and the helium abundance of Saturn, both of which are difficult to determine spectroscopically.

Certification of Compliance with Applicable Executive Orders and U.S. Code

By submitting the proposal identified in this Cover Sheet/Proposal Summary in response to this NRA or AO, the Authorizing Official of the proposing institution (or the individual proposer if there is no proposing institution) as identified below: