Matrix Isolation Studies of Group-IV Oxides. I. Infrared Spectra and Structures of SiO, Si2O2, and Si3O3

Abstract

The matrix isolation of silicon monoxide vapor leads to the formation of at least three distinct species: SiO, Si₂O₂, and Si₃O₃. Infrared absorptions for these molecules are observed at 1223.9 cm⁻¹ (Si¹⁶O); 804.7, 766.3 cm⁻¹ (Si₂¹⁶O₂); 972.6, 631.5, 312.0 cm⁻¹ (Si₃¹⁶O₃). Equations are given for the in‐plane vibrations of the $X_2{Y}_2{\mathrm{(V}}_h)$ ring and the $X_3{Y}_3{\mathrm{(D}}_{\text{3h}})$ ring, and using ¹⁸O substitution, it is shown that these respective models account for the observed ir absorptions of Si₂O₂ and Si₃O₃. Estimates are given for the molecular dimensions of ${\mathrm{Si}}_2{\mathrm{O}}_2{\mathrm{(r}}_{\mathrm{Si–O}}\text{\hspace{0.17em}=\hspace{0.17em}1.71 Å, ∠}\mathrm{OSiO}\text{\hspace{0.17em}=\hspace{0.17em}87°)}$ and ${\mathrm{Si}}_3{\mathrm{O}}_3{\mathrm{(R}}_{\mathrm{Si–O}}\text{\hspace{0.17em}=\hspace{0.17em}1.70 Å, ∠}\mathrm{OSiO}\text{\hspace{0.17em}=\hspace{0.17em}100°)}$ , and for their unobserved vibration frequencies. The reaction SiO + Si₂O₂ → Si₃O₃ is observed during diffusion studies, and a lower limit obtained for the mean bond energy in Si₃O₃ of ∼104 kcal/mole.