10min:

RICK WEHR, A. VITCU, A. D. MAY AND J. R. DRUMMOND, Dept. of Physics, University of Toronto, Toronto, Ontario, Canada, M5S 1A7; R. CIURY\LO, Instytut Fizyki, Universytet Miko\laja Kopernika, Grudziadzka 5/7, 87-100 Torun´, Poland; F. THIBAULT, UMR 6627 du CNRS, Universite de Rennes, Campus de Beaulieu, 34042 Rennes Cedex, France; L. ZHAN AND W.-K. LIU, Dept. of Physics, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1.

The role of inelastic collisions in the formation of infrared spectral line shapes is explored through a comparison of spectroscopic measurements and ab initio calculations. The shapes of a set of CO-Ar spectral lines in the fundamental band were recorded between -50^\circC and +25^\circC, and between 0.05 atm and 1 atm, by a difference-frequency laser spectrometer with a resolution of less than 2 MHz and a signal-to-noise ratio greater than 4000:1. The ab initio line shape calculations used broadening coefficients obtained from fully quantal close-coupled calculations, which were in turn based on an assumed molecular potential energy surface. It is found that a failure to distinguish elastic and inelastic collisions in the CO-Ar system leads to incorrect line shape calculations at low pressures.