Dynamics and kinetics of the Si(1D) + H2/D2 reactions on a new global ab initio potential energy surface

Abstract

Recent studies on the exothermic complex-forming reactions have improved our understanding of complex-forming reactions greatly, however, so far a similar level of study on endothermic ones has been rather limited. In this work, the endothermic complex-forming reaction Si(¹D) + H₂ → SiH + H and its deuterated isotopic variant are investigated by quantum dynamics (QD) and ring polymer molecular dynamics (RPMD) calculations on a new global ab initio potential energy surface (PES) for the ground electronic state, which is constructed based on 8996 symmetry unique points computed at the icMRCI+Q/aug-cc-pVQZ level. The PES reproduces our ab initio data very well in the dynamically important regions, on which the ro-vibrational energy levels of SiH₂ are calculated and general good agreement with experiment is obtained. The integral cross sections and product angular and state distributions are computed in a wide range of collision energies, and interesting dynamics behaviors are revealed. The rate coefficients are also investigated, which display an exponential rise from 2.09 × 10⁻²⁰ to 6.00 × 10⁻¹² cm³ s⁻¹ for the Si(¹D) + H₂ reaction as the temperature increases from 300 to 1500 K, in contrast to the nearly temperature-independent behavior of exothermic complex-forming reactions. In addition, the applicability of the RPMD approach is demonstrated, and the kinetic isotope effect is investigated, the ratio of which decreases from 7.89 (300 K) to 1.70 (1500 K). The effects of tunneling and initial rotational excitation are also discussed.