Theoretical Study of Silicon Monoxide Reactions with Ammonia and Methane

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2017-02, Vol.121 (5), p.1032-1040
• Main Authors: Nguyen, Huyen Thi, Hang, Tran Dieu, Nguyen, Minh Tho
• Format: Article
• Language: English
• Subjects: Barriers; Channels; Chemical bonds; Dehydrogenation; Endothermic reactions; Methane; Silicon; Silicon dioxide
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.6b11665

High-accuracy calculations were performed to study the mechanisms of the reactions between the diatomic silicon monoxide (SiO) with NH3 and CH4. These reactions are relevant to the SiO-related astrochemistry and atmospheric chemistry as well as the activation of the N–H and C–H bonds by the SiO triple bond. Energetic data used in the construction of potential energy surfaces describing the SiO + NH3/CH4 reactions were obtained at the coupled-cluster theory with extrapolation to the complete basis set limit (CCSD­(T)/CBS) using DFT/B3LYP/aug-cc-pVTZ optimized geometries. Standard heats of formation of a series of small Si-molecules were predicted. Insertion of SiO into the N–H bond is exothermic with a small energy barrier of ∼8 kcal/mol with respect to the SiO + NH3 reactants, whereas the C–H bond activation by SiO involves a higher energy barrier of 45 kcal/mol. Eight product channels are opened in the SiO + NH3 reaction including dehydrations giving HNSi/HSiN and dehydrogenations. These reactions are endothermic by 16–119 kcal/mol (calculated at 298.15 K) with the CCSD­(T)/CBS energy barriers of 21–128 kcal/mol. The most stable set of products, HNSi + H2O, was also the product of the reaction pathway having lowest energy barrier of 21 kcal/mol. Ten product channels of the SiO + CH4 reaction including decarbonylation, dehydration, dehydrogenation, and formation of Si + CH3OH are endothermic by 19–118 kcal/mol with the energy barriers in the range of 71–126 kcal/mol. The formation of H2CSiO + H2O has the lowest energy barrier of 71 kcal/mol, whereas the most stable set of products, SiH4 + CO, is formed via a higher energy barrier of 90 kcal/mol. Accordingly, while SiO can break the N–H bond of ammonia without the assistance of other molecules, it is not able to break the C–H bond of methane.