Interatomic Coulombic decay of fixed-in-space neon dimers

Abstract

The detailed theoretical and experimental analysis of the angular distributions of electrons from interatomic Coulombic decay (ICD) of the Ne dimer in the molecular frame is performed. In the initial state the doubly charged dimer ion has one $2s$ vacancy and one $2p$ vacancy on one atom. After the ICD process the neutral neon atom is ionized and the triply charged molecular ion dissociates into singly and doubly charged atomic ions, ${\text{Ne}}^{2+}(2{p}^{\ensuremath{-}2})+{\text{Ne}}^{+}(2{p}^{\ensuremath{-}1})$. From the coincident measurement of kinetic energy release (KER) of the ions and the ICD electron the decay channel can be identified unambiguously. The most detailed experimental data have been obtained for the singlet dicationic state Ne${}^{2+}(2{p}^{\ensuremath{-}2}){[}^{1}\phantom{\rule{-0.16em}{0ex}}D]$. Different KER energies correspond to different internuclear distances at which the ICD process takes place. In experiment the data have been presented for three regions of KER energies, and the corresponding calculations have been performed for three fixed internuclear distances. In calculations we imply that all the electrons in Ne${}_{2}$ to a good approximation are localized. However, we need to retain the molecular character of the dimer wave functions which opens the possibility for the ICD process. To do it, we calculate at first the Hartree-Fock ground state wave functions of the neutral Ne${}_{2}$ dimer using the standard procedure for homonuclear diatomic molecules corresponding to the ${D}_{\ensuremath{\infty}h}$ symmetry group. For the doubly charged ion Ne${}_{2}{}^{2+}$ with two vacancies on one atom the symmetry is lowered to ${C}_{\ensuremath{\infty}v}$, and we are looking now for the set of one-electron Hartree-Fock wave functions which are localized either on the left or on the right atom as a linear combination of symmetry-adopted wave functions. The theory correctly reproduces the experimental data and predicts the sharp variation of the angular distributions as a function of internuclear distance.