The dissociation energy of van der Waals complexes determined by velocity map imaging: values for S0 and S1 p-difluorobenzene–Ar and D0 (p-difluorobenzene–Ar)+

The technique of velocity map imaging, an enhanced resolution variant of ion imaging, is shown to be a useful method for determining the dissociation energy of van der Waals complexes. The method is demonstrated by measuring the dissociation energy of p-difluorobenzene–Ar in the S1 state. From the spectroscopic shift of the S1←S0 transition and the change in the ionisation energy between the complex and free p-difluorobenzene, the dissociation energies in the ground state of the neutral and cationic complexes are determined. The values so determined are 339±4 and 369±4 cm−1 for the S0 and S1 states of the neutral complex, respectively, and 576±4 cm−1 for the cation ground (D0) state.