Modeling the time-resolved Coulomb explosion imaging of halomethane photodissociation with ab initio potential energy...

We present an effective theoretical model to simulate observables in time-resolved two-fragment Coulomb explosion experiments. The model employs the potential energy curves of the neutral molecule and the doubly charged cation along a predefined reaction coordinate to simulate the photodissociation process followed by Coulomb explosion. We compare our theoretical predictions with pump-probe experiments on iodomethane and bromoiodomethane. Our theory successfully predicts the two reaction channels in iodomethane photodissociation that lead to I(P3/22) and I*(P1/22) products, showing excellent agreement with experimental delay-dependent kinetic energy release signals at large pump-probe delays. The theoretical kinetic energy release at small delays depends significantly on the choice of ionic states. By accounting for internal rotation, the kinetic energies of individual fragments in bromoiodomethane align well with experimental results. Furthermore, our theory confirms that two-fragment Coulomb explosion imaging cannot resolve different spin channels in bromoiodomethane photodissociation.