State-to-state vibrational energy transfer in acetylene gas, measured by fluorescence-detected Raman-ultraviolet double resonance spectroscopy

Fluorescence-detected Raman-ultraviolet double resonance spectroscopy enables state-selective investigations of vibrational energy transfer in gas-phase acetylene, C₂H₂. Pulsed coherent Raman excitation of the (ν₂ + ν₄ - ν₄) rovibrational hot band of C₂H₂(g) is followed by rovibronic probing of collision-induced population transfer to the ν₂ vibrational level. This time-resolved spectroscopic technique provides novel kinetic and mechanistic information on the quasi-elastic intermolecular VV transfer process: C₂H₂(ν₂ + ν₄) + C₂H₂(ν = 0) → C₂H₂(ν₂) + C₂H₂(ν₄). The state-to-state second-order rate constant for this process is measured and its relevance to the dynamics of vibrational energy transfer is discussed. The results demonstrate the advantages of rotationally resolved double-resonance tecniques in elucidating vibrational energy transfer processes.