A continuum approach to electron solvation by a layer of polar adsorbates

Multistep and multiscale electron transfer and localization dynamics at a model electrolyte/metal interface

The lifetime, coupling, and localization dynamics of electronic states in molecular films near metal electrodes fundamentally determine their propensity to act as precursors or reactants in chemical reactions, crucial for a detailed understanding of charge transport and degradation mechanisms in batteries. In the current study, we investigate the formation dynamics of small polarons and their role as intermediate electronic states in thin films of dimethyl sulfoxide (DMSO) on Cu(111) using time- and angle-resolved two-photon photoemission spectroscopy. Upon photoexcitation, a delocalized DMSO electronic state is initially populated two monolayers from the Cu surface, becoming a small polaron on a 200 fs time scale, consistent with localization due to vibrational dynamics of the DMSO film. The small polaron is a precursor state for an extremely long-lived and weakly coupled multilayer electronic state, with a lifetime of several seconds, thirteen orders of magnitude longer than the small polaron. Although the small polaron in DMSO has a lifetime of 140 fs, its role as a precursor state for long-lived electronic states could make it an important intermediate in multistep battery reactivity.

Theory of electron localization at dielectric-metal interfaces: A continuum model

Localization of electrons at dielectric-metal interfaces is studied in the framework of a continuum model. The layer of thickness L, with a negative electron affinity, is characterized by the static dielectric constant epsilons and by the optical dielectric constant epsiloninfinity. It is found that the electron localization along the plane of the interface occurs if the layer thickness exceeds a critical value Lc. In the case of a high polar layer, the electron energy of the localized ground state shows a nonmonotonic dependence on the layer thickness. A strong correlation between low-lying excitations and the spread of the localized state has been established. The magnitude of the correlation parameter is close to the analogous correlation for the solvated electron in the bulk. The localization dynamics is discussed in terms of relaxation along a polarization coordinate, which is directly connected to the polarization energy of the layer.

The dynamics of solvation of an electron in the image potential state by a layer of polar adsorbates

Recently, ultrafast two-photon photoemission has been used to study electron solvation at a two-dimensional metalpolar adsorbate interfaces [A. Miller et al., Science 297, 1163 (2002)]. The electron is bound to the surface by the image interaction. Earlier we have suggested a theoretical description of the states of the electron interacting with a two-dimensional layer of the polar adsorbate [K. L. Sebastian et al., J. Chem. Phys. 119, 10350 (2003)]. In this paper we have analyzed the dynamics of electron solvation, assuming a trial wave function for the electron and the solvent polarization and then using the Dirac-Frenkel variational method to determine it. The electron is initially photoexcited to a delocalized state, which has a finite but large size, and causes the polar molecules to reorient. This reorientation acts back on the electron and causes its wave function to shrink, which will cause further reorientation of the polar molecules, and the process continues until the electron gets self-trapped. For reasonable values for the parameters, we are able to obtain fair agreement with the experimental observations.