title: Solvation of Na+, K+, and their dimers in helium.
abstract: Helium atoms bind strongly to alkali cations which, when embedded in liquid helium, form so-called snowballs. Calculations suggest that helium atoms in the first solvation layer of these snowballs form rigid structures and that their number (n) is well defined, especially for the lighter alkalis. However, experiments have so far failed to accurately determine values of n. We present high-resolution mass spectra of Na(+)He(n), K(+)He(n), Na(2)(+)He(n) and K(2)(+)He(n), formed by electron ionization of doped helium droplets; the data allow for a critical comparison with several theoretical studies. For sodium and potassium monomers the spectra indicate that the value of n is slightly smaller than calculated. Na(2)(+)He(n) displays two distinct anomalies at n=2 and n=6, in agreement with theory; dissociation energies derived from experiment closely track theoretical values. K(2)(+)He(n) distributions are fairly featureless, which also agrees with predictions.
authors.affiliation: Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria.
authors.forename: Lukas
authors.initials: L
authors.lastname: An der Lan
authors.forename: Peter
authors.initials: P
authors.lastname: Bartl
authors.forename: Christian
authors.initials: C
authors.lastname: Leidlmair
authors.forename: Roland
authors.initials: R
authors.lastname: Jochum
authors.forename: Stephan
authors.initials: S
authors.lastname: Denifl
authors.forename: Olof
authors.initials: O
authors.lastname: Echt
authors.forename: Paul
authors.initials: P
authors.lastname: Scheier