Mono- and dibridged isomers of Si2H3 and Si2H4: the true ground state global minima. Theory and experiment in concert.

Highly correlated ab initio coupled-cluster theories (e.g., CCSD(T), CCSDT) were applied on the ground electronic states of Si2H3 and Si2H4, with substantive basis sets. A total of 10 isomers, which include mono- and dibridged structures, were investigated. Scalar relativistic corrections and zero-point vibrational energy corrections were included to predict reliable energetics. For Si2H3, we predict an unanticipated monobridged H2Si−H−Si-like structure (Cs, 2A‘ ‘) to be the lowest energy isomer, in constrast to previous studies which concluded that either H3Si−Si (Cs, 2A‘ ‘) or near-planar H2Si−SiH (C1, 2A) is the global minimum. Our results confirm that the disilene isomer, H2Si−SiH2, is the lowest energy isomer for Si2H4 and that it has a trans-bent structure (C2h, 1Ag). In addition to the much studied silylsilylene, H3Si−SiH, we also find that a new monobridged isomer H2Si−H−SiH (C1, 1A, designated 2c) is a minimum on the potential energy surface and that it has comparable stability; both isomers are ...