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 C¹B₂ ← X¹A₁ transition of SiH₂. Moreover, a moderate band observed in the region of 217-236 nm is reduced slightly, which is assigned to the 3¹B₂ ← X¹A₁ 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.