Theory for the short-time response of small Hg n clusters after excitation

Abstract

Abstract. The short-time behavior of small Hg,~ clusters immediately after single or double ionization is studied. We calculate self-consistently the ground state electronic energy E of ionized Hg~ clusters. Upon ionization changes of the potential energy surface (PES) occur, which govern the atomic motion in the cluster. These changes depend on cluster size and charge and are determined by the interplay between the localization of the holes within an ionic core and the polarization energy of the neutral rest of the cluster. In the case of single ionization of the cluster the PES results mainly from hole delocalization. In contrast, in the case of double ionization the PES is governed almost only by strong environment polarization, We use our theory to explain the physical origin of the oscillations in the ionization crosssection of singly and doubly excited Hg~ clusters observed in recent pump-probe experiments.

Real-time observation of ultrafast ionization and fragmentation of mercury clusters

“…Our observation of a similar oscillatory structure in the ionization signal of large singly charged clusters may be due to fragmentation of even larger doubly charged clusters in agreement with Bennemann's result [13]. A Fourier analysis shows that clusters with the same e/m ratio, for instance the clusters Hg + 21 and Hg 2+ 42 , exhibit the same frequency in the short-time oscillatory signal [15].…”

“…Evidence for such a chromophore structure has also been found for the rare gas clusters which are van der Waals bound systems similar to the small Hg-clusters [12]. Calculations based on our data performed by Bennemann and coworkers [13] support such a chromophore model. According to their calculations the ionic cluster has a covalent bound dimer chromophore to which the remaining atoms of the cluster are bound by strong polarization forces.…”

“…This argument applies also for neutral clusters in high Rydberg states which could be the relevant neutral intermediate states in our pump-probe experiments. However, the calculations in [13] are only valid for the van der Waals bound Hg n -clusters or when exciting to the twofold ionic continuum in the case of a covalently bound species.…”

An effective Hamiltonian for an electronically excited solute in a polarizable molecular solvent

“…Studies of the energetics [13,26] and ground-state dynamics [9,14] of I -2 in clusters and in solution combined this description of the charge distribution with empirical potential energy curves of the isolated solute. Localized basis functions (implied by use of a tight binding Hamiltonian) have also been used by Garcia, Bennemann and co-workers to study the dynamics of ionized Hg n clusters [68,69]. However, in their approach, the solute electric ® eld operator is replaced by its expectation value, so that their model corresponds to the`self-consistent' limit in which solute¯uctuations are neglected [25,67], rather than to the adiabatic limit used here.…”

Time-resolved intraband electronic relaxation dynamics of Hgn− clusters (n=7–13,15,18) excited at 1.0 eV

“…Measurements of direct ionization 18,19 and autoionization 20 have been used to investigate subtle developments in ionization potential and absorption spectra with size, revealing marked changes in these properties at relatively small sizes (nϭ13-20). Yet the dynamical consequences of such bonding-type transitions are relatively unexplored 23,24 and are of considerable experimental and theoretical interest. 21 The nonmetal-to-metal transition in mercury clusters is expected to occur at even larger n and has been addressed most directly by Busani et al, 16,22 who extrapolated a 6s-6p band-gap closure at nϳ400Ϯ50 atoms from anion photo-electron ͑PE͒ spectroscopy.…”