Surface Trapped Excess Electrons on Ice

Abstract

Local trapping of excess electrons at the surface of solid water systems has recently been observed in large water clusters and at the ice/vacuum interface. The existence of stable surface-bound states for the excess electron may have important implications in atmospheric chemistry, electrochemistry, and radiation physics. By means of first-principles molecular dynamics we find that excess electrons induce a structural reconstruction of the ice surface on a time scale of a fraction of a picosecond. The surface molecular rearrangement leads to an increase of the number of dangling OH bonds pointing towards the vacuum and to the appearance of an electrostatic barrier preventing the penetration of the electron in the bulk. Both factors imply a remarkable stability for the surface-bound excess electron, with respect to its decay into the bulk solvated state.

Cosmic-ray-driven electron-induced reactions of halogenated molecules adsorbed on ice surfaces: Implications for atmospheric ozone depletion and global climate change

“…Earlier femtosecond time-resolved spectroscopic studies by Wolf's group [64] and Petek's group [65] on thin amorphous ice films (a few monolayers) on a metal or insulator substrate showed lifetimes of less than 1 ps for the presolvated electrons. By first-principles molecular dynamics simulations of the ice surface at the temperatures close to those found in PSCs (150-200 K), Baletto et al [63] found very stable surface-bound states for trapping electron at the ice surface due to the structural rearrangement induced by an excess electron. They proposed that the surface molecular rearrangement leads to an increase of the number of dangling OH bonds pointing towards the vacuum and to the formation of an electrostatic barrier preventing the decay of the electron into the bulk solvated state [63].…”

“…By first-principles molecular dynamics simulations of the ice surface at the temperatures close to those found in PSCs (150-200 K), Baletto et al [63] found very stable surface-bound states for trapping electron at the ice surface due to the structural rearrangement induced by an excess electron. They proposed that the surface molecular rearrangement leads to an increase of the number of dangling OH bonds pointing towards the vacuum and to the formation of an electrostatic barrier preventing the decay of the electron into the bulk solvated state [63]. Most recently, interesting results were reported by Wolf, Bovensiepen and co-…”

“…In 2000s, Researches on electron solvation dynamics and associated dissociative electron transfer reactions of halogenated molecules have continued in water solution [21,[27][28][29][58][59][60][61][62], ice surface [63], ultrathin ice films [16,17,[64][65][66][67] and H 2 O anionic clusters [68][69][70][71][72][73]. Prior to 2008, many experimental and theoretical studies gave very diverse lifetimes and physical natures of e pre states in liquid water [49][50][51][52][53][54][58][59][60][61][62].…”

A Dynamic Landscape from Femtoseconds to Minutes for Excess Electrons at Ice−Metal Interfaces

“…The BLYP exchange-correlation energy functional was used for the neutral structures. In the presence of the excess electron an additional approximate correction for the self-interaction was employed as described and tested in ref 10. The approach we pursue here allows for an interaction of the excess electron with the valence electrons of individual water molecules and hence gives a realistic account of the decay of the excess electron state at a surface trap into the ice layer.…”

“…Once the excess electron is trapped the dynamical creation of orientational defects or other defects can be envisaged. For example a dynamical reorientation of S 1 -molecules, 10 of S A -molecules (as described above), or of S D such that both D atoms are directed toward the excess electron is conceivable, as the corresponding potential energy surface is quite flat. Such a structural evolution of the defects via conformational substates separated by barriers is thermally activated and hence accelerated at increased temperatures in agreement with the experimental observation (see Figure 6b).…”