LIMITS ON THE LIFETIMES OF INTRAMOLECULAR ROVIBRATIONAL RELAXATION

Rotationally resolved infrared laser induced fluorescence spectra are presented for dimethyl ether and methyl formate. Q branch spectra are presented for 1,4???dioxane, methyl formate, and dimethyl carbonate. It has been demonstrated earlier that all of these states intramolecularly vibrationally relax. Lower limits on the lifetime of this process are inferred from the present data. For methyl formate and dimethyl ether the J=1 and 2 states have linewidths <0.31 cm???1. This sets a lower limits on the lifetime of 15 ps, although for the limited number of coupled states an exponential decay is not expected. This is also the lower limit for relaxation in the higher J=20 states of 1,4???dioxane and methyl formate, for which exponential decays probably do occur. Dimethyl carbonate relaxes in greater than 10 ps. All measurements were performed in a pulsed supersonic beam with a infrared optical parametric oscillator