Hindered Coulomb explosion of embedded Na clusters — stopping, shape dynamics and energy transport

Abstract

Abstract. We investigate the dynamical evolution of a Na8 cluster embedded in Ar matrices of various sizes from N = 30 to 1048. The system is excited by an intense short laser pulse leading to high ionization stages. We analyze the subsequent highly non-linear motion of cluster and Ar environment in terms of trajectories, shapes, and energy flow. The most prominent effects are : temporary stabilization of high charge states for several ps, sudden stopping of the Coulomb explosion of the embedded Na8 clusters associated with an extremely fast energy transfer to the Ar matrix, fast distribution of energy throughout the Ar layers by a sound wave. Other ionic-atomic transfer and relaxation processes proceed at slower scale of few ps. The electron cloud is almost thermally decoupled from ions and thermalizes far beyond the ps scale.

Laser-driven nonlinear cluster dynamics

“…Calculations have been performed using TDDFT for Na valence electrons and MD for Na + ions and Ar atoms. From (Fehrer et al, 2007a), with kind permission of The European Physical Journal (EPJ).…”

“…Theoretical analysis has yet to cope with the great variety of material combinations. For an example using the generic test system of metal cluster in a rare gas matrix, see (Fehrer et al, 2007a(Fehrer et al, , 2008. A thorough study of surface-deposited cluster subject to strong laser pulses still is a matter of future studies.…”

Dipole excitations of Ar substrate in contact with Na clusters

“…In order to exemplify the point, we have also plotted in Fig. 8 the actual position of the most external Na ions and this makes the pattern clear, with an effect only along radial coordinate due to the oblate shape of the irradiated cluster [33,34]. Apart from that detail, we find again a dominantly static charge effect explaining the dipole polarizations of Ar atoms, much similar to the deposition case with localization prevailing again and little own dynamics.…”

“…The laser pulse is kept short to concentrate the ionization to a fairly well defined initial time and the intensity is tuned such that the irradiation leaves the cluster with a net 3+ charge. A Coulomb explosion of the cluster is hindered by the matrix which stabilizes that high charge state, but allows a sizable oblate expansion of the cluster [33,34]. The point is illustrated in the upper panel of Fig.…”

“…Such methods are often called quantum-mechanicalmolecular-mechanical (QM/MM) models and have been applied for instance to chromophores in biomolecules [17,18], surface physics [19,20], materials physics [21,22,23,24], embedded molecules [25] and ion channels of cell membranes [26]. We have developed such a QM/MM modeling, primarily in the case of Na in contact with Ar [27,28,29] and successfully applied this method to deposition dynamics on finite Ar clusters [30] or on Ar surfaces [31], as well as to irradiation scenarios in the case of embedded clusters both in the linear (optical response [32]) and non linear (hindered explosion [33,34]) domains. More recently, we have extended the modeling to a MgO substrate [35].…”