Reaction of O(1D) with Silane: Direct Production of SiO

Theoretical Study of Silicon Monoxide Reactions with Ammonia and Methane

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.

Exploring the dynamics of reaction N+SiH(4) with crossed molecular-beam experiments and quantum-chemical calculations

We investigated the reaction N((4)S,(2)D,(2)P)+SiH(4) in crossed molecular beams at a collision energy of 4.7 kcal mol(-1) with a time-of-flight mass spectrometer and selective photoionization. Ion signals were observed at m/z=42-45, associated with two product channels, HSiNH/SiNH(2)+H+H and HSiN/HNSi+H(2)+H. The species producing the signal at m/z=43 is assigned to product HSiN/HNSi and that at m/z=44 to product HSiNH/SiNH(2). The signal observed at m/z=42 is attributed to daughter ions of those two products and that at m/z=45 to (29)Si and (30)Si isotopic variants. We report time-of-flight spectra as a function of laboratory angle and simulations for the two products, from which both kinetic-energy and angular distributions of products in the center-of-mass (c.m.) frame were derived. The dependence of release of kinetic energy on the c.m. scattering angle is weak. The average translational energy released is 7.7 kcal mol(-1) for product channel HSiNH/SiNH(2)+H+H and 30.3 kcal mol(-1) for product channel HSiN/HNSi+H(2)+H. Through consecutive triple fragmentation, the angular distribution is slightly anisotropic for product HSiNH/SiNH(2) but isotropic for product HSiN/HNSi. Assuming equal efficiencies of detection, we estimate the branching ratios of products HSiNH/SiNH(2) and HSiN/HNSi to be roughly 15:85. To facilitate an understanding of the reaction mechanisms, we calculated the potential-energy surface for reaction N((2)D)+SiH(4) with quantum-chemical methods. Reactions N((2)D)+SiH(4)-->SiNH(2)+H+H and N((2)D)+SiH(4)-->HNSi+H(2)+H account satisfactorily for the present experimental results. Isomeric products HSiNH and HSiN are minor in this work.