Quantum Chemical Approach to Interatomic Decay Rates in Clusters

Since their theoretical prediction in 1997, interatomic (intermolecular) Coulombic decay (ICD) and related processes have been in the focus of intensive theoretical and experimental research. The spectacular progress in this direction has been stimulated both by the fundamental importance of the discovered electronic decay phenomena and by the exciting possibility of their practical application, for example, in spectroscopy of interfaces. Interatomic decay phenomena take place in inner-shell-ionized clusters due to electronic correlation between two or more cluster constituents. These processes lead to the decay of inner-shell vacancies by electron emission and often also to the disintegration of the resulting multiple ionized cluster. The primary objective of the theory is, thus, to predict the kinetic energy spectra of the emitted electrons and of the cluster fragments. These spectra are determined by an interplay between the electronic decay process and the nuclear dynamics. Key to the reliable prediction of the observable quantities is the knowledge of the time scale of the interatomic decay. Here we review the recent progress in the development of ab initio quantum chemical methods for the calculation of interatomic decay rates in excited, singly ionized, and doubly ionized systems as well as some of their applications, e.g., to rare gas systems and to endohedral fullerenes.