Quantum and Quasiclassical Dynamics of the S + SD Reaction: Role of Reagent Vibrational Excitation

The S(³P) + SD(X²Π) reaction is investigated on the ground electronic HS₂ potential energy surface (PES) using time-dependent wave packet (TDWP) and quasiclassical trajectory (QCT) methods. Initial state-selected reaction probabilities and integral cross sections are calculated for abstraction and exchange channels at collision energies up to 0.10 eV. Both channels proceed without an entrance barrier through an intermediate complex, with abstraction being the dominant pathway owing to the high stability of S₂. The role of reactant vibrational excitation is examined for ν = 0, 1, 3, 5, and 10, with j = 0. For ν = 0, the quantum results agree well with the classical trajectories, indicating the reaction is governed primarily by classical forces. A QCT/QM-αJ extrapolation scheme is assessed against full quantum results and provides an efficient and reliable approach for estimating integral cross sections while retaining essential quantum effects. For the exchange channel, the quantum cross sections show a gradual enhancement at higher collision energies from ν = 1, while the abstraction channel shows this enhancement only from ν = 5 onward. At ν = 10, they stop decreasing: the abstraction cross section increases with collision energy, whereas the exchange cross section levels off. These results demonstrate that quantum effects become important at high vibrational excitation.