Ultrafast photodissociation dynamics of dichloromethane on three-dimensional potential energy surfaces and its Coulomb explosion signature.

We present efficient and reliable molecular dynamics simulations of the photodissociation of dichloromethane, followed by Coulomb explosion. These simulations are performed by calculating trajectories on accurate potential energy surfaces of the low-lying excited states of the neutral dichloromethane molecule. The subsequent time-resolved Coulomb explosions are simulated on the triply charged ionic state, assuming Coulomb interactions between ionic fragments. The dominant reaction channel of photoexcited dichloromethane is CH2Cl + Cl two-body dissociation with simultaneous excitation of the CH2Cl rotation, which is clearly identified from the Coulomb explosion observables. Both the neutral state trajectories and the simulated Coulomb explosion observables indicate that intra-molecular photoisomerization of dichloromethane is unlikely to occur. Estimating the kinetic energy release using ab initio ionic potential reveals a discrepancy of ∼5-8 eV compared to our simulated values using Coulomb potential. The molecular structural changes during photodissociation are clearly mapped to the ionic-fragment coincidence signals, demonstrating the Coulomb explosion imaging technique as a powerful tool to probe the time-resolved reaction dynamics.