Modeling the coincident three-ion momentum imaging of diiodomethane photodissociation on reduced-dimensional potential energy surfaces

We present an efficient theoretical model to simulate observables in the time-resolved coincident three-ion Coulomb explosion experiment of diiodomethane. The model employs two degrees of freedom to describe the C–I bond breaking and the CH2I rotation during photodissociation and three degrees of freedom to describe the coincident CH2++I2++I2+ fragmentation during the subsequent Coulomb explosion. By solving the equations of motion, the photodissociation pathways are obtained on two-dimensional potential energy surfaces of the valence excited states of the neutral molecule, and the asymptotic momenta of the three ionic fragments are determined on the three-dimensional ground-state potential energy surface of the fivefold-charged cation. The photodissociation pathways are consistent with previous ab initio molecular dynamics simulations and indicate a CH2I rotational period of ∼340 fs. The theoretical time-resolved kinetic energy release and the correlation between the kinetic energy release and the angle between the two I2+ momenta show good agreement with experimental signals in part, reflecting and confirming the static CH2I2 state and the CH2I + I dissociation channels.