Vibrational-vibrational and vibrational-translational/rotational processes in methane, oxygen gas-phase mixtures

Abstract

Various methane-oxygen mixtures of different compositions and total pressures were studied optoacoustically for vibrational-vibrational and vibrational-rotational/translational characteristics. V-R, T rates for CH₄-CH₄ and CH₄-O₂ were measured as respectively 0·645 and 0·105 μs^-1 atm^-1. The rate-constants for transfer between the CH₄(v ₂, v ₄) bending modes and the oxygen fundamental, v, are 12±2 μs^-1 atm^-1 for v→(v ₂, v ₄) and 1.1 ± 0·2 μs^-1 atm^-1 for (v ₂, v ₄)→v. The excitation was to CH₄(v ₃) with a He-Ne laser and, following very fast equilibration with CH₄(v ₁), three routes of deactivation were followed in O₂ collisions; (i) to the CH₄(2v ₄) level and thence by CH₄ collisions to the v ₄ fundamental, (ii) to the O₂ overtone (2v), followed by the O₂ intermolecular process to the fundamental, and (iii) to the O₂ fundamental plus one CH₄ bending mode. Rate constants for routes (i), (ii) and (iii) are given.