Nuclear-Spin-Dependent Photodissociation Dynamics of H2S+ via the A 2A1(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-JH2 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.