Full characterization of OH product energetics in the reaction of O(1D2) with hydrocarbons

Abstract

The energetics of the OH(X ²Π, 0≤ν‘≤4) product arising from the reaction of O(¹D₂) with the hydrocarbons CH₄, C₂H₆, C₃H₈, and C(CH₃)₄ was fully characterized using laser‐induced fluorescence (LIF). The product distribution is in sensible accord with earlier more limited LIF and infrared chemiluminescence studies, and the overall yield of OH decreases dramatically in the case of the heavier hydrocarbons as would be expected if dissociation of the collision intermediate was dominated by rupture of the relatively weak C–C bond. The energetics of the O(¹D₂)/CH₄ reaction suggest that it proceeds via an insertion/elimination reaction, while that of O(¹D₂) with the heavier hydrocarbons appears to involve two parallel mechanisms. The major channel yields vibrationally and rotationally cool OH; by comparison with abstraction of hydrogen by O(³P_J) which preferentially yields vibrationally excited OH, this channel is associated with dissociation of a long‐lived complex. The highly excited component of OH population arises from a prompt dissociation of a collision complex prior to statistical distribution of reaction exothermicity among its internal modes.