Vibrational Relaxation of the 2ν₅ Overtone of CDCl₃ Following Tea CO₂ Laser Excitation of the ν₄ Mode

Abstract

The time variation of the 2ν₅ fluorescence intensity was measured in CDCl₃ excited in the ν₄ C–D bending mode by a TEA CO₂ laser operating on the 10P(48) line. A fast rise of the fluorescence, with a time constant ≤ 1 μs Torr, was first observed, showing that a fast equilibration of population occurs between the ν₄ and ν₅ modes through a ν₄ ↔ ν₅ Coriolis-assisted intermode transfer and a ν₅ ↔ 2ν₅ near-resonant ladder-climbing process. Then a first fast fluorescence decay was observed and attributed to a (ν₄, ν₅) → ν₂ intermode transfer with a rate constant of (7.10 ± 1.13)ms^-1 Torr^-1. At last, a much slower decay, with a rate constant of 0.111 ± 0.015 ms^-1 Torr^-1, results from the less efficient intermode transfer and V–T,R deexcitation processes involving the ν₃ and ν₆ states, and which compete to relax the gas to a thermodynamic equilibrium.