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 (E_coll = 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 Ų at E = 0.5 kcal mol^-1 to a plateau near 4.9 Ų above E = 6 kcal mol^-1. At fixed collision energies the large translational fraction (f_T = 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 (〈n_bend〉 ≈ 3.6-5.0, peaking at E = 0.5 kcal mol^-1) over the stretches (〈n_sym〉 ≈ 1.1-4.1, 〈n_asym〉 ≈ 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.