THE DETECTION OF FAST NEUTRAL FRAGMENTS FOLLOWING THE PHOTODISSOCIATION OF KRYPTON CLUSTER IONS

Mass and kinetic energy resolved krypton cluster ions, Kr-n(+), have b een photodissociated in the entrance to a time-of-flight (TOF) device of variable length. The subsequent deflection of all ions allowed for time resolved measurements to be undertaken on the neutral photofragme nts. Following the absorption of a photon (hv=2.33 eV), all cluster io ns up to Kr-25(+) were found to eject one or, possibly, two neutral at oms with relatively high kinetic energies. An analysis of the laser po larization dependence of this event showed that the atoms are ejected on a time scale which is short compared with the rotational period of a cluster (10-100 ps). Remaining internal energy within the cluster io ns is dissipated through the further loss of neutral atoms, but with l ow kinetic energies. The latter process is found to be; isotropic with respect to the angle of polarization of the laser radiation. Kinetic energy releases calculated from the TOF spectra exhibit a gradual decl ine as a function of cluster size out as far as Kr-13(+) and, thereaft er, maintain a constant value. This pattern of behavior is significant ly different from that observed previously [Smith et al., J. Chem. Phy s. 97, 397 (1992)] for argon cluster ions, Ar-n(+). A careful analysis of the kinetic energy data for Kr-3(+) photodissociation reveals that , in at least one of the reaction paths, the Kr+ fragment can only be formed in the ground spin-orbit state. This observation implies that p hotofragmentation proceeds via a 1(1/2)(g)<--1(1/2)(u) transition. The implications of this result for the analogous AT(3)(+) photofragmenta tion are discussed.