			15min:

MEASUREMENT OF ROTATIONAL STATE-TO-STATE RELAXATION COEFFICIENTS BY RAMAN-RAMAN DOUBLE RESONANCE. APPLICATION TO SELF-COLLISIONS IN ACETYLENE..

J. L. DOMENECH, R. Z. MARTINEZ AND D. BERMEJO, Instituto de Estructura de la Materia (CSIC), Serrano 123, E-28006 Madrid, SPAIN.

We have developed a technique for the measurement of state-to-state rotational relaxation rates due to collisions in the gas phase. A single J state of the v₂=1 vibrational level of acetylene is populated by a Stimulated Raman process. After a variable delay of a few ns we record high resolution ( sim 0.003 cm^-1) spectra of the Q-branch of the v₂=2 leftarrow v₂=1 transition by a second Stimulated Raman process. The relative intensities of the lines of this Q-branch, recorded as a function of the the initially pumped J level and the number of collisions between the pump and probe stages (delay × pressure product), allows us to obtain a set of state-to-state energy transfer coefficients by fitting the evolution of the observed populations to that predicted by a master equation with adjustable coefficients.

The experimental details and first results for odd-J levels of acetylene at 150 K will be presented.