Direct observation of the dynamics of electronic excitations in molecules and small clusters

Femtosecond time-resolved photoelectron spectroscopy is applied to study re laxation paths of excited states of mass-selected negatively charged cluste rs. As a first example, the lifetime of an excited state of the carbon trim er anion is measured directly. In addition, the mechanism of the decay, i.e ., the configurations of the participating electronic states, is determined From the photoelectron spectra. In general, this method can be used to stu dy all kinds of electronic excitation and relaxation processes in mass-sele cted nanoparticles.