Reaction dynamics of OH + SiH4 → H2O + SiH3: a quasi-classical trajectory study on the PES-2022 surface.

A quasi-classical trajectory (QCT) study is presented of the OH + SiH4 → H2O + SiH3 hydrogen-abstraction reaction on the full-dimensional analytical potential energy surface PES-2022. A total of 1.8 million trajectories were run at seven fixed collision energies (Ecoll = 0.5, 1, 2, 4, 6, 8, and 10 kcal mol-1), yielding more than 28 000 reactive trajectories after discrete zero-point energy filtering (DZPE; see Section 2.2). The integral reactive cross section σ(E) rises from 0.56 Å2 at E = 0.5 kcal mol-1 to a plateau near 4.9 Å2 above E = 6 kcal mol-1. At fixed collision energies the large translational fraction (fT = 0.58-0.80) is characteristic of the direct abstraction mechanism at high collision energy. The differential cross sections are strongly forward/sideways peaked at low energy and shift toward a dominant stripping contribution above E ≥ 4 kcal mol-1. Normal-mode analysis of the H2O product reveals preferential excitation of the bending mode (〈nbend〉 ≈ 3.6-5.0, peaking at E = 0.5 kcal mol-1) over the stretches (〈nsym〉 ≈ 1.1-4.1, 〈nasym〉 ≈ 0.65-3.5). The strong negative correlation between scattering angle θ and impact parameter b (r ≤ -0.85) confirms the predominantly direct character of the abstraction at all energies studied.