INTRAMOLECULAR VIBRATIONAL-RELAXATION IN DIMETHYL ETHER

Abstract

Intramolecular vibrational energy transfer in isolated gas phase molecules of dimethyl ether 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 3050 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 the C–H stretches are strongly mixed with nearby bath states. The observed energy content distribution is best described by a statistical model which assumes coupling over a 20 cm−1 range. Dilution factors for the various C–H stretch modes were observed which vary from 0.01 to 0.20. These values are dependent on the rotational state excited. The experiments are performed by exciting a molecule cooled in a nozzle expansion with light from an infrared optical parametric oscillator. The fluorescence spectra are recorded with a cryogenic Michelson interferometer.