Gas-Phase Synthesis of the Elusive Trisilicontetrahydride Species (Si₃H₄)

The bimolecular gas-phase reaction of ground-state atomic silicon (Si; ³P) with disilane (Si₂H₆; ¹A_1g) was explored under single-collision conditions in a crossed molecular beam machine at a collision energy of 21 kJ mol^-1. Combined with electronic structure calculations, the results suggest the formation of Si₃H₄ isomer(s) along with molecular hydrogen via indirect scattering dynamics through Si₃H₆ collision complex(es) and intersystem crossing from the triplet to the singlet surface. The nonadiabatic reaction dynamics can synthesize the energetically accessible singlet Si₃H₄ isomers in overall exoergic reaction(s) (-93 ± 21 kJ mol^-1). All reasonable reaction products are either cyclic or hydrogen-bridged suggesting extensive isomerization processes from the reactants via the initially formed collision complex(es) to the fragmenting singlet intermediate(s). The underlying chemical dynamics of the silicon-disilane reaction are quite distinct from the isovalent carbon-ethane system that does not depict any reactivity at all, and open the door for an unconventional gas phase synthesis of hitherto elusive organosilicon molecules under single-collision conditions.