HIGH RESOLUTION, HIGH DILUTION SPECTRA OF OCS IN Ar, N2, AND Xe VALERIE

Author Institution: Jet Propulsion Labs; Department of Chemistry, Dartmouth CollegeWe have used high resolution $(0.01 cm^{-1})$ FTIR spectroscopy to measure the spectrum of OCS isotopomers in natural abundance in Ar, Xe, and N2 matrices at dilutions as high as 1:96,000 in the $2000 cm^{-1}$ region (the nominal CO stretch region). Over the temperature range 10 - 30 K, we find very different behavior to the positions of the absorptions and their widths. Most striking is a narrowing of widths with increasing temperature in Ar, but a broadening in $N_{2}$. At these dilutions, the true ``matrix isolation limit'' to the spectra can be attained: viz.single sharp $(FWHM-0.04 cm^{-1})$ features for each isotopomer. Annealing induces irreversible changes that are sensitive probes of the solute-solvent interactions. A potential energy model for these interactions will be discussed that can rule out certain assignments to new features and illuminate the origin of the shift in absorption frequency when OCS is taken from the gas phase to the matrix phase. The model also allows identification of the origin of the two features seen in Xe spectra as two readily identifiable matrix sites