Ultraschnelle Relaxation optisch angeregter Elektronen in kleinen Übergangsmetallclustern

In the present dissertation the relaxation dynamics of optically excited electrons in free Ni3, Pd3, Pd4, Pd7, and Pt3 has been investigeted. By means of femtosecond pump-probe photoelectron spectroscopy the electronic relaxations in these small transition metal clusters could be observed for the first time in real-time . A quantitative analysis of the data reveals inelastic electron-electron relaxation times in the order of magnitude of 10 to 100 femtoseconds . These unexpected short electronelectron- scattering times are caused by the relatively large density of states in the vicinity of the highest occupied cluster orbital. This large density of states results from the narrow bandwidth of the partially filled d-levels in the transition metal clusters . Other aspects for the enhancement of inelastic electron-electron scattering are the spread of the electronic levels by vibrational broadening and the spill-out of the s/p-electron wave functions intensifying the Coulomb-interaction between the electrons