Photodissociation Dynamics of H 2 S via the 3 1 A ′ State: Dominance of Dual Intersection-Induced Barriers

Hydrogen sulfide (H2S), a major sulfur carrier in the interstellar medium, undergoes ultraviolet photodissociation that shapes interstellar sulfur chemistry and sulfur isotope fractionation. Here we construct a four-state diabatic potential energy matrix for the lowest four 1A' states of H2S using high-level ab initio data and a neural-network-based diabatization scheme. Quantum wave packet dynamics on the 31A' state reproduce the main experimental features of the H + SH(X2Π/A2Σ+) internal energy distributions at 143.15 nm, with minor discrepancies likely due to the unaccounted contributions of 1A″ states. Trajectory surface-hopping simulations show that H2S undergoes transient trapping in a basin formed by dual intersection-induced barriers on the 21A' surface. This dual-barrier topology restricts dissociation to a narrow escape pathway along the bond-angle coordinate, promoting SH(A2Σ+) formation. The results reveal a new mechanism in which dual intersection-induced barriers govern product branching in high-lying electronic states.