15min:

J. L DOMENECH, R. Z. MARTINEZ, D. BERMEJO, Instituto de Estructura de la Materia (CSIC), Dept. of Molecular Pysics, Serrano 123, E-28006 Madrid, Spain.

The quasi -cw stimulated Raman technique is a powerful tool for the determination of collisional broadening and line-mixing parameters, which bear a very direct relationship with the rotational energy transfer rate constants matrix at the state-to-state level. Indeed, the broadening coefficients and the analysis of line-mixing profiles, frequently combined with a rate-law analysis, have provided a wealth of information on collision physics for many gas systems throughout the years. We report on new high resolution measurements of the broadening coefficients on the Q-branch of the ₂ band of acetylene.

.2cm Furthermore, last year at this meeting, we reported on a new technique for the determination of state-to-state rotational energy transfer rate constants. based on a time-resolved double-resonance Raman-Raman scheme. It uses the quasi -continuous stimulated Raman-loss technique for the probe stage. Through a systematic recording of the time evoultion of rotational populations from a single initially pupulated J level, it allows the direct determination of most elements of the rate-constant matrix without resorting to fitting or scaling laws.

.2cm The comparison of the results obtained from from the high resolution spectroscopic approach with those from the time-resolved dynamics experiment provides insight into the collision mechanisms and some of the assumptions or simplifications usually made in rate-law analysis.