Unusual insertion mechanism in the reaction C(³P) + H₂ → CH + H

We use quasiclassical trajectories to study the reaction C(³P) + H₂ → CH + H using an accurate ab initio potential surface, making comparisons with recent product distribution measurements. An analysis of the reactive trajectories indicates that the formation of CH + H is completely dominated by insertion to form a ³CH₂ intermediate. However, this C insertion is initiated from nearly linear C-H-H geometries rather than by perpendicular attack as has been found for other insertion reactions (like O(¹D) + H₂). Perpendicular insertion collisions do occur, but they are almost always nonreactive due to poor coupling between modes initially excited in ³CH₂ and the product reaction coordinate (C-H stretch). The calculated product rovibrational distributions are in excellent agreement with experiment, but we find that they are not sensitive to the presence of this modified insertion mechanism. Reactions like O(¹D) + H₂ may also show the modified insertion mechanism at high energies. Results from C + HD and C + HCl are also examined.