Electron hydration: interface shells

Interface water cluster anions (H2O)n− (n ⩽ 12) composed of two to four fragments are simulated in the unrestricted Hartree–Fock approximation with the second order Moeller–Plesset perturbation theory corrections taken into account with the 6-31++G** basis set either augmented or not with the floating center of eight s functions. A linear dependence of the circumsphere radius involving central molecules of the anions on 1/n provides an estimate of the excess electron radius in condensed water (about 2.5 Å). Vertical detachment energies, approximated with linear dependences on n−1/3, are extrapolated to the values around 3.4 eV for bulk water.