Theoretical exploration of femtosecond multi-state nuclear dynamics of small clusters

We investigate ultrafast multi-state nuclear dynamics in a triatomic cluster. In particular, we explore how the intracluster nuclear dynamics of the ${\mathrm{Ag}}_{\mathrm{3}}^{\mathrm{-}}{\mathrm{/Ag}}_{\mathrm{3}}{\mathrm{/Ag}}_{\mathrm{3}}^{\mathrm{+}}$ system is reflected in the femtosecond pump-probe negative ion-to neutral-to positive ion (NENEPO) signals. The nuclear dynamics is based on classical trajectories on the ground electronic adiabatic state potential hypersurfaces obtained from accurate ab initio quantum chemistry calculations. The nuclear dynamics of ${\mathrm{Ag}}_{\mathrm{3}}$ initiated from the linear transition state involves distinct sequential processes of configurational relaxation to the triangular configuration, intracluster collisions, and the onset of IVR, resonant, and dissipative IVR, and vibrational equilibration. We determined the timescales for these processes and discussed their dependence on the initial 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) NENEPO signal. We show how geometrical change, completion of IVR and vibrational coherence effects can be identified in the NENEPO signals. A comparison of the calculated NENEPO signals with the available experimental data is presented.