Photodissociation Pathways of Methanol: Dissociation, Roaming, and Migration

In this joint experimental and theoretical study, we examine the two-body photodissociation pathways induced in deuterated methanol by both single and double laser pulses. The measurements were conducted using IR pump-IR probe spectroscopy paired with the coincident momentum imaging technique. Our work unambiguously shows the roaming behavior of a D₂ neutral resulting in D₂⁺, which is a strong pathway after direct excitation to a dication. Two pulse measurements reveal that despite the low formation probability, the migration pathways occur fastest of any photodissociation relaxation route. To elucidate the mechanistic origin of the observed fragmentation channels, we performed ab initio molecular dynamics simulations based on DFT for ground-state reactivity and state-averaged CASSCF for excited-state dynamics, enabling direct comparison with experimental yields.