Bonn 2000 – wissenschaftliches Programm
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MO: Molekülphysik
MO 15: Poster I: Cluster und Fullerene
MO 15.8: Poster
Mittwoch, 5. April 2000, 10:30–13:00, Aula
Ultrafast Fragmentation and Vibrational Dynamics of Small Alkali and Alkali Halide Clusters — •A. Bartelt, P. Rosendo-Francisco, S. Minemoto, C. Kaposta, B. Baptist, C. Lupulescu, S. Vajda, and L. Wöste — Institut für Exp.-physik, FU Berlin, Arnim allee 14, D-14195 B erlin
With the one-color femtosecond pump&probe technique the dynamics of predissociated excited states of isotope-selected trimers, K3, K2Na, and Na2K, were studied in molecular beams. The transient cation signals of the parent clusters show an exponential decay which represents the lifetime of the populated excited states. The excitation wavelength dependence (730-840 nm) of the lifetimes was determined (6,5-10 ps for K3, 2.9-5.2 ps for K2Na, and 2,5-6 ps for Na2K). From the time resolved signal of the emerging fragment ions, the dominant fragmentation channels were identified as well. In the case of the mixed trimer Na2K, the femtosecond vibrational dynamics of the excited state and of the fragment ion was resolved. These clusters may serve as model systems for controlled fragmentation studies.One possible method of controlling the fragmentation is the use of shaped pulse forms. For this purpose, we built up a programmable pulse shaper and developed an optimization feedback-loop. Shaping of the laser pulse is achieved by a liquid crystal modulator. An optimization algorithm based on evolutionary strategies drives the modulator to achieve an optimal pulse form, which guides the molecules into a fragmentation channel. In this contribution, we will present our first results on the dynamics of nonstochiometric heterogeneous sodium-fluoride clusters NanFn−1.