Competing Si₂CH₄-H₂ and SiCH₂-SiH₄ Channels in the Bimolecular Reaction of Ground-State Atomic Carbon (C(³P_j)) with Disilane (Si₂H₆, X¹A_1g) under Single Collision Conditions

The bimolecular gas-phase reaction of ground-state atomic carbon (C(³P_j)) with disilane (Si₂H₆, X¹A_1g) was explored under single-collision conditions in a crossed molecular beam machine at a collision energy of 36.6 ± 4.5 kJ mol^-1. Two channels were observed: a molecular hydrogen elimination plus Si₂CH₄ (reaction 1) pathway and a silane loss channel along with the formation of SiCH₂ (reaction 2), with branching ratios of 20 ± 3 and 80 ± 4%, respectively. Both channels involved indirect scattering dynamics via long-lived Si₂CH₆ reaction intermediate(s); the latter eject molecular hydrogen and silane in “molecular” elimination channels within the rotational plane of the fragmenting intermediate nearly perpendicularly to the total angular momentum vector. These molecular elimination channels are associated with tight exit transition states as reflected in a significant electron rearrangement as visible from the chemical bonding in the light reaction products molecular hydrogen and silane. Once these hydrogenated silicon-carbide clusters are formed within the inner envelope of carbon stars such as of IRC + 10216, the stellar wind can drive both Si₂CH₄ and SiCH₂ to the outside sections of the envelope, where they can be photolyzed. This is of particular importance to unravel potential formation pathways to disilicon monocarbide (Si₂C) observed recently in the circumstellar shell of IRC + 10216.