Vibrational Energy Transfer in Methane

Abstract

The asymmetric stretching vibration ν3 of methane has been excited by a chopped He–Ne laser. The phase shift of infrared emission from the asymmetric stretch and from the infrared-active bend ν4 has been measured as a function of chopping frequency and gas pressure. Vibrational relaxation times have been found for the removal of energy from the asymmetric stretch (pτ = 7.0 ± 1 nsec·atm), for the appearance of this energy in the ν4 bend (pτ = 5 + 3, −2 nsec·atm), and for the relaxation of vibrational energy into translational and rotational energy (pτ = 1.90 ± 0.10 μsec·atm). The mechanism and rates of V → V energy transfer are compared to calculations for a repulsive intermolecular potential. The general applicability of the laser-excited vibrational fluorescence method and the interpretation of phase-shift data are discussed.