Isomerization of SiOH +, HSiOH and H 2SiO: a density functional study

Abstract

Density functional theory (DFT) is used to investigate the isomerization reactions of SiOH +, and of HSiOH. Linear SiOH + is predicted to be more stable than linear HSiO + by 65.1 kcal mol −1. This energy difference becomes 63.5 kcal mol −1 after zero-point vibrational energy (ZPVE) correction. The barrier height for the endothermic isomerization is predicted to be 96.7 kcal mol −1 (93.1 kcal mol −1 after ZPVE correction). The calculated total energies for HSiOH (cis), HSiOH (trans) and H 2SiO are very close to each other. HSiOH (trans) is predicted to be more stable than the cis-isomer by 0.2 kcal mol −1. HSiOH (trans) is predicted to be more stable than H 2SiO by 2.0 kcal mol −1. Zero-point vibrational energy correction changes the relative stability of HSiOH (cis) and HSiOH (trans) by making the cis-isomer to be more stable than the trans-isomer (0.02 kcal mol −1). ZPVE correction decreases the energy difference between HSiOH (trans) and H 2SiO but does not lead to a reversal of relative stabilities. The predicted barrier height for HSiOH (cis) → HSiOH (trans) reaction is 8.1 kcal mol −1. A much larger barrier height (56.3 kcal mol −1) is predicted for the reaction H 2SiO → HSiOH (trans). Calculated equilibrium geometries, activation energies and vibrational frequencies are shown to be in good agreement with the results of high quality ab initio studies.