Seminars Archive

Real-time dynamics of alkali-doped helium nanodroplets

Abstract


Tuesday, July 19, 2005, 11:00


Seminar Room

Sincrotrone Trieste, Basovizza
Real-time dynamics of alkali-doped helium nanodroplets


Frank Stienkemeier

(Physikalisches Institut, Universitt Freiburg)
Abstract
In recent years helium nanodroplet isolation has been shown to be an extraordinary tool in molecular spectroscopy. In our experiments we have combined this method with femtosecond pump-probe techniques to study the real-time dynamics of doped superfluid helium nanodroplets. In particular, the formation of alkali-helium exciplexes upon electronic excitation of the alkalis is followed in real time. We observe quantum interference structures both in the ionization rates of desorbed single atoms as well as exciplex molecules. Analysis of the interference oscillations reveals a detailed view of the level structure of the molecules during formation, providing a novel approach to characterize vibrational structures and dynamics of transient species. Furthermore we use helium nanodroplet isolation to form small alkali clusters. The alkalis are picked up successively by the helium droplets in order to aggregate to clusters at temperatures of 380 mK. Fragmentation times of these clusters upon electronic excitation are determined. In contrast to earlier experiments on free potassium clusters, we find substantially longer times in the fragmentation processes. Results using different droplet sizes demonstrate that energy is dissipated into the helium environment on ps time scales and in this way a fast fragmentation of the alkali clusters is inhibited.