Abstract

Time resolved IR-UV double resonance spectroscopy enables state-selective kinetic studies of rotationally resolved vibrational energy transfer in gas phase acetylene-d₂ (C₂D₂). As a prime example, C₂D₂/Ar collisions are found to equilibrate laser-induced populations in the 4₁5₁ vibrational level with the neighboring 4₂ and 5₂ levels, prior to significant transfer to the lower 4₁ and 5₁ levels. This vibrational bottleneck effect is attributable to the high efficiency of quasielastic intramolecular V−V energy transfer relative to V−T,R processes. In the contrasting case of C₂D₂ self-collisions, quasielastic intermolecular V−V energy transfer relieves the bottleneck. Relevant second-order rate constants have been measured, and selectivity with regard to angular momenta and state symmetries identified. Other related experiments aim to demonstrate ways in which intramolecular perturbations contribute to collision-induced rovibrational energy transfer, with potential for enhancement of laser-induced photochemistry. Novel experimental strategies, including Raman−UV double resonance¹ and implementation of a narrowband optical parametric oscillator,² are also being used in this context.

© 1991 Optical Society of America