Cohesive energies of K+n 5<n<200 from photoevaporation experiments

Evaporative cooling of internal energy rich potassium cluster ions K+n (5<n<200) is investigated within two well defined but quite different time windows. One of the time windows starts 1 μs after the photoexcitation of the cluster ions isolates one step in the evaporative cooling cascade. The experimental technique insures the complete determination of the dissociation channels. Tandem time-of-flight mass spectroscopy measures the relative rate of competing dissociation channels from ion fragmentation patterns. The corresponding neutral fragments are unambiguously determined after the reionization. Values for the dissociation energies of K+n (up to n=25) have been deduced from the unimolecular dissociation rates using statistical methods. These values are compared to Hückel calculations. The second time window starting just after the reexcitation of mass selected K+n is used to follow the steps of the photoinduced sequential evaporation from ‘‘hot’’ clusters. The photofragmentation patterns for several photon energies give the atomization energies of ionized clusters up to n=200. Their evolution vs 1/R is compared to the droplet model.