Selective dissociation of HCl in Kr from vibrational overtones

Vibrational levels v = 1, 2, and 3 of HCl in Kr matrices are populated with tunable IR radiation and the excited molecules are dissociated by UV excitation to the repulsive A (1)Pi state. Cl fragments are recorded by laser induced fluorescence of Kr2Cl and dissociation rates are determined from the increase in LIF with UV dose. The enlarged UV Franck-Condon range for overtones allows the study of cage exit of H fragments with small kinetic energy E-kin. A threshold at E-kin = 1.4 eV and a steep rise indicate a predominant sudden exit. Monomers, different initial rotational states and transients in the relaxation cascade are preselected with overtone excitation and the feasibility of a discrimination between isotopes, aggregates, and local structures is illustrated. (C) 2002 American Institute of Physics.