STATE-TO-STATE VIBRATIONAL-ENERGY TRANSFER IN ACETYLENE GAS, MEASUREDBY FLUORESCENCE-DETECTED RAMAN ULTRAVIOLET DOUBLE-RESONANCE SPECTROSCOPY

Fluorescence-detected Raman-ultraviolet double resonance spectroscopy enables state-selective investigations of vibrational energy transfer in ps-phase acetylene, C2H2. Pulsed coherent Raman excitation of the ( nu2 + nu4 - nu4) rovibrational hot band of C2H2(g) is followed by rovi bronic probing of collision-induced population transfer to the nu2 vib rational level. This time-resolved spectroscopic technique provides no vel kinetic and mechanistic information on the quasi-elastic intermole cular V-V transfer ProcesS: C2H2(nu2 + nu4) + C2H2 (nu = 0) --> C2H2 ( nu2) + C2H2(nu4). The state-to-state second-order rate constant for th is process is measured and its relevance to the dynamics of vibrationa l energy transfer is discussed. The results demonstrate the advantages of rotationally resolved double-resonance techniques in elucidating v ibrational energy transfer processes.