Mechanism and dynamics of excited-state atom (Si (¹D), O(¹D), C(¹D)) reactions

Reactions involving electronically excited atoms (Si(¹D), C(¹D) and O(¹D) are considered here) play a critical role in atmospheric, combustion, and interstellar chemistry. Three kinds of typical excited-state atom reactions which are endothermic, exothermic, and thermoneutral respectively, are compared in this work. First, the dynamics of the Si(¹D) + H₂ reaction and its deuterated isotopic variants have been investigated via the quasiclassical trajectory method on a recent global ab initio potential energy surface constructed by us. Integral cross sections, differential cross sections, and product state distributions are computed over a wide range of collision energies, and the results obtained by the Gaussian binning procedure are in good agreement with the quantum dynamics results. Our analysis reveals rich dynamical features. Notably, trajectories with lifetimes shorter than 10 fs shows markedly different behavior compared to longer-lived complex-forming trajectories. The contribution of these short-lived trajectories becomes increasingly significant at higher collision energies and is further enhanced by rotational excitation of the H₂ reactant. A comparative study indicates that the temperature dependence of rate coefficients for the Si(¹D)+H₂ reaction is distinctly different from those of the C(¹D) + H₂ and O(¹D) + C₂H₄ → CH₃+HCO reactions, and the reaction mechanisms also display different features for the three types of reactions.