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.