Seminars Archive
Real-time dynamics of alkali-doped helium nanodroplets
Abstract
Tuesday, July 19, 2005, 11:00
Seminar Room
Real-time dynamics of alkali-doped helium nanodroplets
Frank Stienkemeier
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.
