Vibrational distribution of CH3 produced by the reaction of O(1D2) atom with CH4

Abstract

The nascent vibrational distribution of CH3 produced by the reaction O(1D2)+CH4→OH+CH3 (ΔH0=−182 kJ mol−1) has been investigated by infrared diode laser kinetic spectroscopy. The reaction was initiated by the generation of O(1D2) atoms by excimer laser photolysis of N2O or O3 at a total pressure of 200 mTorr, and the ν2 (out-of-plane bending) bands of CH3, v2=1←0 up to 4←3, were measured as functions of time. The vibrational distribution of ν2 (v≤3) was found to be noninverted and much less excited than a prior distribution. The fraction of the available energy released to the ν2 vibration, <fv(CH3ν2)≳, is estimated to be about 0.019. A similar noninverted vibrational distribution of CH3 was observed in the reaction of CH4 with O(3P) (ΔH0=8 kJ mol−1), which is known to be a direct hydrogen abstraction reaction. The results may suggest that the CH3 moiety is gradually relaxed to a planar structure during these reactions.