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

Abstract: 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 characterize the C-I bond breaking and the $\text{CH}_2\text{I}$ rotation during photodissociation, and three degrees of freedom to characterize the coincident $\text{CH}_2^{+}+\text{I}^{2+}+\text{I}^{2+}$ fragmentation during the following Coulomb explosion. By solving the equation of motion, the photodissociation paths are uncovered on two-dimensional potential energy surfaces of the A-band excited states of the neutral molecule and the asymptotic momenta of the three ionic fragments are obtained on the three-dimensional ground-state potential energy surface of the five-fold charged cation. The photodissociation paths are consistent with previous ab initio molecular dynamics simulations and indicate the $\text{CH}_2\text{I}$ rotational period to be around 340 fs. The theoretical time-dependent kinetic energy release and the correlation between the kinetic energy release and the angle between the two $\text{I}^{2+}$ momenta show good agreement with the experimental signals in parts, which reflects and confirms the static $\text{CH}_2\text{I}_2$ state and the $\text{CH}_2\text{I}+\text{I}$ dissociation channels.