Precursor of the I aq− charge-transfer-to-solvent (CTTS) band in I−⋅(H2O)n clusters

Ultraviolet charge-transfer-to-solvent (CTTS) bands are general spectral features of inorganic salts dissolved in dipolar (e.g., aqueous) solvents. The bands originate from excitations of the anions, and the excited states are thought to involve a delocalized electronic state supported by the arrangement of solvent molecules around the ion in the ground state. These diffuse states have fascinated physical chemists since the 1930s, who first used continuum models to explain the phenomenon and then later refined the treatment to include local molecular interactions. In this paper, we report that CTTS bands evolve from features present in very small gas phase clusters, I−⋅(H2O)n, n=1–4, and discuss how localization of the continuum wave function of the ejected electron acts as a precursor to the bound excited state in the liquid.