Theoretical exploration of stationary and of ultrafast spectroscopy of small clusters

Stationary spectra offer information on the interplay between the structure s and the nature of electronic excitations reflecting bonding properties, a s shown by comparing Si-n with Ag-n (n = 4 - 6) clusters. In order to study the dynamical properties, simulations and analysis of femtosecond (fs) tim e-resolved pump-probe or pump-dump signals have been carried out, which all ows us to determine the timescales and the nature of configurational change s versus internal vibrational relaxation (IVR) in electronic ground or exci ted states. For this purpose we have developed a multi-state ab initio mole cular dynamics (involving ground as well as adiabatic or non-adiabatic exci ted electronic states) on the timescale of the nuclear motion, using the ti me evolution of a thermal ensemble in the Wigner representation. The combin ation of ab initio quantum-chemical methods used for the molecular dynamics 'on the fly' and the Wigner-distribution approach for the description of t he motion of the nuclei also allowed the accurate determination of pump-pro be and pump-dump signals under temperature-dependent initial conditions. We use this novel combination of methods to investigate the dynamics in excit ed states of non-stoichiometric NanFn-1 clusters with a single excess elect ron. The timescales of the structural relaxation in excited states versus i ntramolecular vibrational relaxation processes have been determined, as ill ustrated for the example of Na4F3. This is the first study of the system wi th 15 degrees of freedom for which the dynamics in the excited states has b een carried out without the precalculation of the energy surfaces.