title: A Study of H2O2 with Threshold Photoelectron Spectroscopy (TPES) and Electronic Structure Calculations: Redetermination of the First Adiabatic Ionization Energy (AIE).
abstract: In this work, hydrogen peroxide has been studied with threshold photoelectron (TPE) spectroscopy and photoelectron (PE) spectroscopy. The TPE spectrum has been recorded in the 10.0-21.0 eV ionization energy region, and the PE spectrum has been recorded at 21.22 eV photon energy. Five bands have been observed which have been assigned on the basis of UCCSD(T)-F12/VQZ-F12 and IP-EOM CCSD calculations. Vibrational structure has only been resolved in the TPE spectrum of the first band, associated with the X̃(2)Bg H2O2(+) ← X̃(1)A H2O2 ionization, on its low energy side. This structure is assigned with the help of harmonic Franck-Condon factor calculations that use the UCCSD(T)-F12a/VQZ-F12 computed adiabatic ionization energy (AIE), and UCCSD(T)-F12a/VQZ-F12 computed equilibrium geometric parameters and harmonic vibrational frequencies for the H2O2 X̃(1)A state and the H2O2(+) X̃(2)Bg state. These calculations show that the main vibrational structure on the leading edge of the first TPE band is in the O-O stretching mode (ω3) and the HOOH deformation mode (ω4), and comparison of the simulated spectrum to the experimental spectrum gives the first AIE of H2O2 as (10.685 ± 0.005) eV and ω4 = (850 ± 30) and ω3 = (1340 ± 30) cm(-1) in the X̃(2)Bg state of H2O2(+). Contributions from ionization of vibrationally excited levels in the torsion mode have been identified in the TPE spectrum of the first band and the need for a vibrationally resolved TPE spectrum from vibrationally cooled molecules, as well as higher level Franck-Condon factors than performed in this work, is emphasized.
authors.affiliation: IOM-CNR Tasc Laboratory , SS-14, Km 163.5, Area Science Park, 34149 Basovizza, Trieste, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Schio
authors.affiliation: IOM-CNR Tasc Laboratory , SS-14, Km 163.5, Area Science Park, 34149 Basovizza, Trieste, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Alagia
authors.affiliation: LIBPhys-UNL, Laboratory for Instrumentation, Biomedical Engineering and Radiation Physics, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa , Caparica, Portugal.
authors.forename: Antonio A
authors.initials: AA
authors.lastname: Dias
authors.affiliation: Dipartimento di Ingegneria Civile ed Ambientale, Università di Perugia , 06125 Perugia, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Falcinelli
authors.affiliation: Department of Physics, University of Gothenburg , 41296 Gothenburg, Sweden.
authors.forename: Vitali
authors.initials: V
authors.lastname: Zhaunerchyk
authors.affiliation: School of Chemistry, University of Southampton , Highfield, Southampton SO17 1BJ, United Kingdom.|Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University , Hung Hom, Hong Kong.
authors.forename: Edmond P F
authors.initials: EP
authors.lastname: Lee
authors.affiliation: Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University , Hung Hom, Hong Kong.
authors.forename: Daniel K W
authors.initials: DK
authors.lastname: Mok
authors.affiliation: School of Chemistry, University of Southampton , Highfield, Southampton SO17 1BJ, United Kingdom.
authors.forename: John M
authors.initials: JM
authors.lastname: Dyke
authors.affiliation: IOM-CNR Tasc Laboratory , SS-14, Km 163.5, Area Science Park, 34149 Basovizza, Trieste, Italy.|Department of Chemistry and Drug Technologies, Sapienza University , P.le A. Moro 5, 00185 Rome, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Stranges