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MO: Fachverband Molekülphysik
MO 23: Molekülphysik Poster 2
MO 23.1: Poster
Thursday, March 5, 2009, 16:30–19:00, VMP 8 Foyer
Alkali-helium snowballs formed on helium nanodroplets — Severin Müller, •Raphael Katzy, Marcel Mudrich, and Frank Stienkemeier — Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany
Ions implanted in suprafluid helium significantly influence the surrounding quantum liquid. The strong electric field gradient exerted by the charge induces a severe increase in the helium density leading to the localization of helium atoms in layers around the ion. Since the density in these layers commonly exceeds the one of solid helium, such structures are named snowballs. Monte Carlo calculations provide numbers of helium atoms N1 for shell closures around alkali ions [1].
We systematically study the formation of alkali-helium snowballs Ak1,2+HeN (Ak=Na, K, Rb, Cs). Helium nanodroplets are multiply loaded with alkali atoms before being photo-ionized by a Ti:Sa fs laser. The distribution of snowballs Ak1,2+HeN is analyzed by means of a quadrupole mass spectrometer. The experimental data show snowball formation around all investigated alkali species. Agreement of N1 with theoretical predictions is found in the case of Rb+ and Cs+. Evidence of a subshell closure for Cs+ is explained in line with single-atom evaporative energies taken from theory.
[1] M. Rossi, M. Verona, D.E. Galli, L. Reatto: Phys. Rev. B, 69:212510, 2004.