title: Direct determination of the ionization energies of FeO and CuO with VUV radiation.
abstract: Photoionization efficiency curves were measured for gas-phase FeO and CuO using tunable vacuum-ultraviolet radiation at the Advanced Light Source. The molecules are prepared using laser ablation of a metal-oxide powder in a novel high-repetition-rate source and are thermally moderated in a supersonic expansion. These measurements provide the first directly measured ionization energy for CuO, IE(CuO)=9.41 +/- 0.01 eV. The direct measurement also gives a greatly improved ionization energy for FeO, IE(FeO) = 8.56 +/- 0.01 eV. The ionization energy connects the dissociation energies of the neutral and cation, leading to a refined bond strength for the FeO cation: D0(Fe(+)-O)=3.52 +/- 0.02 eV. A dramatic increase in the photoionization cross section at energies of 0.36 eV above the threshold ionization energy is assigned to autoionization and direct ionization involving one or more low-lying quartet states of FeO+. The interaction between the sextet ground state and low-lying quartet states of FeO+ is key to understanding the oxidation of hydrogen and methane by FeO+, and these experiments provide the first experimental observation of the low-lying quartet states of FeO+.
authors.affiliation: Department of Chemistry, University of Massachusetts Amherst, Massachusetts 01003, USA. rbmetz@chemistry.umass.edu
authors.forename: Ricardo B
authors.initials: RB
authors.lastname: Metz
authors.forename: Christophe
authors.initials: C
authors.lastname: Nicolas
authors.forename: Musahid
authors.initials: M
authors.lastname: Ahmed
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Leone
mesh_terms: D003198:Computer Simulation; D003300:Copper / Q000737:chemistry* / Q000528:radiation effects*; D005290:Ferric Compounds / Q000737:chemistry* / Q000528:radiation effects*; D018499:Linear Energy Transfer; D008956:Models, Chemical; D008958:Models, Molecular; D011829:Radiation Dosage; D011839:Radiation, Ionizing; D014466:Ultraviolet Rays
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide; D003300:Copper; C030973:cupric oxide