Nuclear-Spin-Dependent Photodissociation Dynamics of H2S+ via the A2A1(2, 9, 0) State

Abstract

Nuclear spin symmetry imposes rigorous selection rules on the rotational levels accessible to molecules with identical nuclei, potentially influencing nonadiabatic dynamical pathways. Here, we investigate this role in the state-selected photodissociation of H₂S⁺ via the A²A₁ (2, 9, 0) state using time-sliced velocity map imaging of ortho- and para-enriched parent cations. Our results show strict conservation of nuclear spin symmetry, with H₂ co-fragments selectively populating odd- and even-J_H2 states. Critically, fragment angular distributions exhibit a pronounced dependence on the parent’s nuclear spin symmetry. This highlights competition between the A²A₁ → B²B₂ → 1⁴A₂ and 1²A′ → 1⁴A″ dissociation pathways, governed strongly by nuclear spin, independent of rotational excitation. Furthermore, co-activating the symmetric stretching mode (v₁) alongside the bending mode (v₂) amplifies these symmetry-dependent differences. These findings reveal a vibrational-mode-specific coupling that actively steers nonadiabatic transition probabilities in molecular dissociation.