Observation of the reactive potential-energy surface of the Ca–HX* system through van der Waals excitation

The potential-energy surface of the excited-state reactions of calcium with halogen halides has been explored by the optical excitation of a Ca–HX van der Waals complex prepared in a supersonic expansion. Resonances and intense vibrational progressions of van der Waals modes have been observed, and the spectra have been analysed on a local-mode basis. It is seen that the excitation promotes modes involving the Ca–HCl bending coordinate, which appears to be different from the reaction coordinate.