Collision induced intramolecular vibrational energy exchange in1B3u(n,pgr;ast;) pyrazine was investigated by analyzing the pressure dependence of the emission from 10 prepared single vibronic levels. Energy transfer rates are, in general, lower than those previously observed in electronic excited states. Though the magnitude of the energy defect for a process strongly influences the transfer rate, other propensity rules are important. Among the single quantum changes possible, those involving mode 16b predominate. The vibronic coupling to the upper1B2u(pgr;,pgr;ast;) state increases the observed rates dramatically.
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