Are Nonadiabatic Reaction Dynamics the Key to Novel Organosilicon Molecules? The Silicon (Si(3P))-Dimethylacetylene (C4H6(X1A1g)) System as a Case Study.

The bimolecular gas phase reaction of ground-state silicon (Si; 3P) with dimethylacetylene (C4H6; X1A1g) was investigated under single collision conditions in a crossed molecular beams machine. Merged with electronic structure calculations, the data propose nonadiabatic reaction dynamics leading to the formation of singlet SiC4H4 isomer(s) and molecular hydrogen (H2) via indirect scattering dynamics along with intersystem crossing (ISC) from the triplet to the singlet surface. The reaction may lead to distinct energetically accessible singlet SiC4H4 isomers (1p8-1p24) in overall exoergic reaction(s) (-107-20+12 kJ mol-1). All feasible reaction products are either cyclic, carry carbene analogous silylene moieties, or carry C-Si-H or C-Si-C bonds that would require extensive isomerization from the initial collision complex(es) to the fragmenting singlet intermediate(s). The present study demonstrates the first successful crossed beams study of an exoergic reaction channel arising from bimolecular collisions of silicon, Si(3P), with a hydrocarbon molecule.