Interatomic Coulombic decay

Interatomic Coulombic decay (ICD) is an electronic decay process that is particularly important for those inner-shell or inner-subshell vacancies that are not energetic enough to give rise to Auger decay. Typical examples include inner-valence-ionized states of rare gas atoms. In isolated systems, such vacancy states are bound to decay radiatively on the nanosecond timescale. A rather different scenario is realized whenever such a low-energy inner-shell-ionized species is let to interact with an environment, for example, in a cluster. In such a case, the existence of the doubly ionized states with positive charges residing on two different cluster units leads to an interatomic (or intermolecular) decay process in which the recombination part of the two-electron transition takes part on one unit, whereas the ionization occurs on another one. ICD [73-75] is mediated by electronic correlation between two atoms (or molecules). In clusters of various sizes and compositions, ICD occurs on the timescale from hundreds of femtoseconds [18] down to several femtoseconds [76-79]. 

S. Marburger, O. Kugeler, U. Hergenhahn, T. Moller, Experimental evidence for interatomic Coulombic decay in Ne clusters, Phys. Rev. Lett. 90 (2003) 203401. 

T. Jahnke, A. Czasch, M.S. Schoffler, S. Schossler, A. Knapp, M. Kasz, J. Titze, C. Wimmer, K. Kreidi, R.E. Grisenti, A. Staudte, O. Jagutzki, U. Hergenhahn, H. Schmidt-Bocking, R. Dorner, Experimental observation of interatomic Coulombic decay in neon dimers, Phys. Rev. Lett. 93 (2004) 163401. 

N. Vaval, L.S. Cederbaum, Ab initio lifetimes in the interatomic Coulombic decay of neon clusters computed with propagators, J. Chem. Phys. 126 (2007) 164110. 

In this section we will provide the formalism for an extension of the Born-Oppenheimer adiabatic approximation that deals with unstable autoioniz-ing molecules and takes into account the coupling between electronic and nuclear motion. The new formalism will be applied in two cases (i) full collision process of vibrational excitation of H2 molecule by electron impact [8], (ii) half collision process of interatomic Coulombic decay of electronically excited Ne cationic dimer [9,10]. 

In conclusion, the repulsive interactions arise from both a screened coulomb repulsion between nuclei, and from the overlap of closed inner shells. The former interaction can be effectively described by a bare coulomb repulsion multiplied by a screening function. The Moliere function, Eq. (5), with an adjustable screening length provides an adequate representation for most situations. The latter interaction is well described by an exponential decay of the form of a Bom-Mayer function. Furthermore, due to the spherical nature of the closed atomic orbitals and the coulomb interaction, the repulsive forces can often be well described by pair-additive potentials. Both interactions may be combined either by using functions which reduce to each interaction in the correct limits, or by splining the two forms at an appropriate interatomic distance . 

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