Hamburg 2009 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

MO: Fachverband Molekülphysik

MO 23: Molekülphysik Poster 2

MO 23.1: Poster

Donnerstag, 5. März 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 Ak_1,2⁺He_N (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 Ak_1,2⁺He_N 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.