Far-UV Absorption Spectra of SiH2 and Dibridged Si2H2 Isolated in Solid Argon

We employ electron bombardment during the deposition of an Ar matrix containing a small proportion of SiH4 to generate various silicon hydrides. Subsequently, the irradiation of a matrix sample at 365 nm decomposes SiH2 and dibridged Si2H2 in solid Ar, which we identify through infrared spectroscopy. We further recorded the corresponding ultraviolet absorption spectra at each experimental stage. An intense band observed in the range of 170-203 nm is largely destroyed upon 365-nm photolysis, which is assigned to the C 1B2 & LARR; X 1A1 transition of SiH2. Moreover, a moderate band observed in the region of 217-236 nm is reduced slightly, which is assigned to the 3 1B2 & LARR; X 1A1 transition of dibridged Si2H2. These assignments are made based on the observed photolytic behavior, and the prediction of the vertical excitation energies with the corresponding oscillator strengths by using time-dependent density functional theory and equation-of-motion coupled cluster theory.