Collision induced intersystem crossing in methylene on reactive surfaces: application of a new technique to CH2(a 1A1) + H2

Abstract

The ratio, β, of the rate of collision induced intersystem crossing (CIISC) to the total rate of removal, has been determined for CH₂(a¹A₁) + H₂. ¹CH₂ was generated from ketene by laser flash photolysis at 308 nm. ³CH₂, formed directly by photolysis or by CIISC with either He or H₂, was probed by LIF on conversion to OH by reaction with NO. The total relative yields of ³CH₂ were determined from an analysis of the time dependence of pairs of OH time profiles, obtained in the presence and absence of H₂, at a total pressure of 10 Torr, with a helium buffer gas and at 295 K. The hydrogen pressure was varied over the range 0–1.2 Torr. Corrections were made to the profiles for differential quenching of the OH LIF signals. A value of β = 0.10_−0.04^+0.10 was obtained from a global analysis of the data and from analysis of pairs of profiles.