title: Valence Electronic Structure of Aqueous Solutions: Insights from Photoelectron Spectroscopy.
abstract: The valence orbital electron binding energies of water and of embedded solutes are crucial quantities for understanding chemical reactions taking place in aqueous solution, including oxidation/reduction, transition-metal coordination, and radiation chemistry. Their experimental determination based on liquid-photoelectron spectroscopy using soft X-rays is described, and we provide an overview of valence photoelectron spectroscopy studies reported to date. We discuss principal experimental aspects and several theoretical approaches to compute the measured binding energies of the least tightly bound molecular orbitals. Solutes studied are presented chronologically, from simple electrolytes, via transition-metal ion solutions and several organic and inorganic molecules, to biologically relevant molecules, including aqueous nucleotides and their components. In addition to the lowest vertical ionization energies, the measured valence photoelectron spectra also provide information on adiabatic ionization energies and reorganization energies for the oxidation (ionization) half-reaction. For solutes with low solubility, resonantly enhanced ionization provides a promising alternative pathway.
authors.affiliation: Institute of Methods for Material Development, Helmholtz-Zentrum Berlin, D-12489 Berlin, Germany; email: robert.seidel@helmholtz-berlin.de , bernd.winter@helmholtz-berlin.de.
authors.forename: Robert
authors.initials: R
authors.lastname: Seidel
authors.affiliation: Institute of Methods for Material Development, Helmholtz-Zentrum Berlin, D-12489 Berlin, Germany; email: robert.seidel@helmholtz-berlin.de , bernd.winter@helmholtz-berlin.de.
authors.forename: Bernd
authors.initials: B
authors.lastname: Winter
authors.affiliation: Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482; email: stephen.bradforth@usc.edu.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Bradforth
mesh_terms: D004247:DNA / Q000737:chemistry; D004573:Electrolytes / Q000737:chemistry; D004583:Electrons; D007477:Ions / Q000737:chemistry; D009711:Nucleotides / Q000737:chemistry; D056951:Photoelectron Spectroscopy / Q000379:methods*; D012492:Salts / Q000737:chemistry; D012996:Solutions; D028561:Transition Elements / Q000737:chemistry; D014867:Water / Q000737:chemistry*
chemical_list: D004573:Electrolytes; D007477:Ions; D009711:Nucleotides; D012492:Salts; D012996:Solutions; D028561:Transition Elements; D014867:Water; D004247:DNA
keywords: electron binding energies; hydration; ionization; liquid jet; photodetachment