THEORETICAL EXPLORATION OF FEMTOSECOND MULTISTATE NUCLEAR-DYNAMICS OFSMALL CLUSTERS

We investigate ultrafast multi-state nuclear dynamics in a triatomic c luster. In particular, we explore how the intracluster nuclear dynamic s of the Ag-3(-)/Ag-3/Ag-3(+) system is reflected in the femtosecond p ump-probe negative ion-to neutral-to positive ion (NENEPO) signals. Th e nuclear dynamics is based on classical trajectories on the ground el ectronic adiabatic state potential hypersurfaces obtained from accurat e ab initio quantum chemistry calculations. The nuclear dynamics of Ag -3 initiated from the linear transition state involves distinct sequen tial processes of configurational relaxation to the triangular configu ration, intracluster collisions, and the onset of IVR, resonant, and d issipative IVR, and vibrational equilibration. We determined the times cales for these processes and discussed their dependence on the initia l cluster temperature. The Wigner representation of the density matrix was utilized to simulate the NENEPO-zero kinetic energy (NENEPO-ZEKE) signal and the total (integrated over the photoelectron energy) NENEP O signal. We show how geometrical change, completion of IVR and vibrat ional coherence effects can be identified in the NENEPO signals. A com parison of the calculated NENEPO signals with the available experiment al data is presented. (C) 1998 American Institute of Physics.