A Study of H2O2 with Threshold Photoelectron Spectroscopy (TPES) and Electronic Structure Calculations: Redetermination of the First Adiabatic Ionization Energy (AIE)

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• 作者：Luca Schio ; Michele Alagia ; Antonio A. Dias ; Stefano Falcinelli ; Vitali Zhaunerchyk ; Edmond P. F. Lee ; Daniel K. W. Mok ; John M. Dyke ; Stefano Stranges
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：July 14, 2016
• 年：2016
• 卷：120
• 期：27
• 页码：5220-5229
• 全文大小：417K
• 年卷期：0
• ISSN：1520-5215

文摘

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 X̃²B_g H₂O₂⁺ ← X̃¹A 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 X̃¹A state and the H₂O₂⁺ X̃²B_g 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 X̃²B_g 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.