Dresden 2000 – wissenschaftliches Programm
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PV: Plenarvorträge
PV IX
PV IX: Plenarvortrag
Mittwoch, 22. März 2000, 14:30–15:00, H 01
New aspects in the spectroscopy of clusters — •Michel Broyer — Laboratoire de Spectrométrie ionique et moléculaire, Université Claude Bernard, Bât 205, 43 Bd du 11 Novembre, 69622 Villeurbanne Cedex, France — Träger des Gentner-Kastler-Preises
The spectroscopy of clusters has to overcome at least two main difficulties. Firstly the very short lifetimes of the excited states and the fragmentation phenomena preclude a detailed robivronic analysis of the observed bands. Moreover the clusters are very often non rigid and this results in too complex spectra. We will present recent measurements using different approaches in spectroscopic investigations. In the case of metal clusters, typically from 500 to 6000 atoms are deposited and embedded in a transparent matrix. The size effects on the plasmon frequency are clearly evidenced and interpreted by sophisticated theoretical calculations. The relaxation time of the excitation is measured by femtosecond pumpp probe experiments in collaboration with the group of F. Vallee. Two relaxation times are clearly observed, the shorter corresponding to the electronic thermalization and the longer to the ions thermalization (vibronic relaxation). The electronic realxation time is strongly size dependent and this point will be discussed.
An other approach consists to measure directly the properties of the fundamental state. In this respect, the measurements of the electric polarizability and the electric dipole are performed by deviation experiments. As an illustration, we discuss the case of KC60, where the potassium atom may move on the surface of the fullerene. A strong electric dipole exists because the valence electron of the K atom tends to be transfered to the C60 molecule. At high temperature, the K atom becomes less mobile, a correlation time for these thermal fluctuations is measured and at very low temperature the K atom bcomes locked on the fullerene surfacedue; due to the rotation of the molecule no more averaged dipole is opbtained.