The Infrared Spectrum of Disilane

Abstract

The infrared absorption spectrum of Si₂H₆ gas has been observed from 350 to 4000 cm^—1. Four of the five infrared active fundamentals have been found and assigned (ν₅ and ν₆, ‖ bands at 2154.4 and 842.7 cm^—1; ν₇ and ν₈, ⊥ bands at 2181.1 and 945.7 cm^—1). The Q branches of ν₇ and ν₈ were observed with moderate dispersion and the spacings measured as 2.43₅ and 3.42 cm^—1. These spacings are consistent with the Coriolis interaction in a symmetric top without internal rotation, but they do not agree with the spacings predicted by assuming free internal rotation. The general appearance of ν₇ and ν₈ in disilane is similar to these bands in ethane, suggesting comparable potential barriers to internal rotation. In the course of the experiments it was found that disilane decomposes slowly at room temperature into SiH₄ and that in the preparation of disilane from Si₂Cl₆, the Si–Si bond is cleaved by an excess of LiAlH₄, producing SiH₄.