Dispersion Stabilization of Solvated Electrons and Dipole-Bound Anions

Abstract

It has long been assumed that stability of “solvated electrons” and dipole-bound anions results primarily from the static Coulomb interaction of an excess electron with charge distribution of the neutral molecular host. Our results indicate, however, that the dispersion interaction between the loosely bound electron and the neutral molecular host is as important as the static Coulomb stabilization. A perturbation scheme is designed to analyze physically meaningful components of electron binding energy, and highly correlated electronic structure results are presented for dipole-bound anions and solvated electrons in the (HF) n clusters (n ) 2, 3). The vertical electron detachment energy for (HF)3 was found to be 0.63 and 0.21 eV for the solvated electron and dipole-bound anion, respectively. The equilibrium zigzag geometrical structure of the dipole-bound anion differs drastically from the cyclic C3h structure of the neutral trimer. The dispersion interaction is commonly associated with an attractive component of van der Waals interactions that displays asymptotic R -6 behavior, where R is the distance between interacting species. 1 As recognized by London, the dispersion effect results from correlated fluctuations of electron charge densities of interacting atomic or molecular species. 2 In this contribution we discuss the role of dispersion interaction in a different molecular context. We consider a loosely bound electron (lbe) as a chemical species, and we discuss its interaction with the neutral molecular host as if we were dealing with a weakly bound molecular dimer. Our theoretical framework applies to dipole-bound states (dbs) of molecular anions and to “solvated electrons” (se) because these anions share a feature that the excess electron is bound by physical rather than chemical interactions with its neutral molecular host. 3 The results presented here extend our earlier observations about the role of dynamic electron correlation in dipole-bound anions, 4-6 in particular in systems with hydrogen bonds such as (HF)2 - 7