title: Ion induced snowballs as a diagnostic tool to investigate the caging of metal clusters in large helium droplets.
abstract: Metal clusters embedded in ultracold helium nanodroplets are exposed to femtosecond laser pulses with intensities of 10(13)-10(14) W/cm2. The influence of the matrix on the ionization and fragmentation dynamics is studied by pump-probe time-of-flight mass spectrometry. Special attention is paid to the generation of helium snowballs around positive metal ions (Me(z+)He(N), z=1,2). Closings of the first and second helium shells are found for silver at N(1)=10,12 and N(2)=32,44, as well as for magnesium at N1=19-20. The distinct abundance enhancement of helium snowballs in the presence of isolated atoms and small clusters in the droplets is used as a diagnostics to explore the cage effect. For silver, a reaggregation of the clusters is observed at 30 ps after femtosecond laser excitation.
authors.affiliation: Institut für Physik, Universität Rostock, Universitätsplatz 3, 18051 Rostock, Germany.
authors.forename: Tilo
authors.initials: T
authors.lastname: Döppner
authors.forename: Thomas
authors.initials: T
authors.lastname: Diederich
authors.forename: Sebastian
authors.initials: S
authors.lastname: Göde
authors.forename: Andreas
authors.initials: A
authors.lastname: Przystawik
authors.forename: Josef
authors.initials: J
authors.lastname: Tiggesbäumker
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Meiwes-Broer