Rovibrational energy transfer in the 4νCH manifold of acetylene, viewed by IR-UV double resonance spectroscopy. 3. State-to-state J-resolved kinetics

Time-resolved infrared-ultraviolet double resonance (IR-UV DR) spectroscopy is used to study the kinetics of collision-induced state-to-state molecular energy transfer between rovibrational states in the 12700-cm^-1 4ν_CH manifold of the electronic ground state of acetylene (C ₂H₂). Particular initial and final rovibrational J-states are prepared and monitored by a pair of tunable laser pulses (IR PUMP and UV PROBE) and the kinetic results recorded by continuously varying the time delay between those pulses at a set sample pressure. After allowing for collision-induced quenching of fluorescence and mass transfer from the IR-UV optical excitation zone (by beam fly out and diffusion), an array of kinetic data for J-resolved energy-transfer channels can be interpreted by means of a mechanistically structured master-equation model. This paper focuses on kinetics derived by probing C₂H₂ in its 4ν_CH J=12 state (which is affected by intramolecular perturbations and implicated in unusual collision-induced quasi-continuous background effects) and J-resolved collision-induced rovibrational energy transfer with both even ΔJ and (supposedly forbidden) odd ΔJ.