Gas-Phase Formation of the Disilavinylidene (H₂ SiSi) Transient

The hitherto elusive disilavinylidene (H₂ SiSi) molecule, which is in equilibrium with the mono-bridged (Si(H)SiH) and di-bridged (Si(H₂ )Si) isomers, was initially formed in the gas-phase reaction of ground-state atomic silicon (Si) with silane (SiH₄ ) under single-collision conditions in crossed molecular beam experiments. Combined with state-of-the-art electronic structure and statistical calculations, the reaction was found to involve an initial formation of a van der Waals complex in the entrance channel, a submerged barrier to insertion, intersystem crossing (ISC) from the triplet to the singlet manifold, and hydrogen migrations. These studies provide a rare glimpse of silicon chemistry on the molecular level and shed light on the remarkable non-adiabatic reaction dynamics of silicon, which are quite distinct from those of isovalent carbon systems, providing important insight that reveals an exotic silicon chemistry to form disilavinylidene.