INTRAMOLECULAR VIBRATIONAL-RELAXATION IN 1,4 DIOXANE

Abstract

Intramolecular vibrational energy transfer in isolated gas phase molecules of dioxane has been studied by spectrally resolving the IR laser induced fluorescence from C–H stretch fundamentals, combination bands, and overtones in the region from 2800 to 3000 cm−1. By comparing the experimentally observed relative energy content of the IR active modes with that calculated from a statistical model it is concluded that substantial randomization of the energy initially deposited in the zeroth order optically excited state occurs. This statistical distribution differs from a thermal distribution due to fluctuations in the local state density. The energy content distribution is best described by the model if coupling over a range of 4 cm−1 is assumed. Dilution factors for the various C–H stretch modes were observed which vary from 0.018 to 0.13. These values are dependent on the rotational state excited. Collisional time dependent spectra of several relaxed modes are presented. The experiments are performed by exciting molecules cooled in a nozzle expansion with light from an infrared optical parametric oscillator. The fluorescence spectra are recorded with a cryogenic Michelson interferometer.