Radical Ions in Liquids

Abstract

The interaction of ionizing radiation-fast electrons, a-particles, x-and ')'-rays, and ultraviolet (UV) and vacuum ultraviolet (VUV) photons-with molecular solids and liquids causes the formation of short-lived electron-hole pairs that, in such media, thermalize and, eventually, localize yielding and/or (solvated) and holes (see Chaps. 1-5). The distinction between the anions and the is arbitrary. For the time being, it will be assumed that radical ions have an excess electron or deficiency in the valence orbitals of a single solvent molecule (molecular ions or monomer ions) or a small group of such molecules (dimer ions or multimer ions) that do not share charge with neutral solvent molecules that solvate them. Naturally, the excess in a anion is indistinguishable from other valence in this anion. By contrast, in the solvated electron (also' known as electron, see Chap. 7), the density resides mainly iIi interstitial sites between the solvent molecules (solvation cavity) that are polarized by the charge at its center (thereby forming the outer shell of a negative polaron). The underlying assumption of this visualization is that the is a single-electron state whose properties can be given by a band model in which the valence in the solvent and the excess in the cavity are wholly separately treated [1]-in the exact opposite way to how the electronic structure of the solvent ion is viewed. An additional assumption is usually made that the excess electron interacts with (rigid, flexible, or polarizable) solvent molecules by means of an empirical classical potential. Both of these simplifying assumptions find little support in structural studies of trapped electrons in vitreous molecular solids using magnetic resonance spectroscopy [2].