A Study of H2O2with Threshold Photoelectron Spectroscopy (TPES) and Electronic Structure Calculations: Redetermination of the First Adiabatic Ionization Energy (AIE)

Luca Schio, Michele Alagia, Antonio A. Dias, Stefano Falcinelli, Vitali Zhaunerchyk, Edmond P.F. Lee, Kam Wah Mok, John M. Dyke, Stefano Stranges

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4 Citations (Scopus)


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 X2BgH2O2+← X1A H2O2ionization, 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 H2O2X1A state and the H2O2+X2Bgstate. 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 H2O2as (10.685 ± 0.005) eV and ω4= (850 ± 30) and ω3= (1340 ± 30) cm-1in the X2Bgstate 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.
Original languageEnglish
Pages (from-to)5220-5229
Number of pages10
JournalJournal of Physical Chemistry A
Issue number27
Publication statusPublished - 14 Jul 2016

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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