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.