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.