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Updated: May 22, 2025

High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
Published on: June 28, 2016
Direct Observation of a Fundamental Arylium Species Using Photoelectron Spectroscopy: Singlet-Triplet Gap in
Megan R Bentley1,2, Ugo Jacovella1, Jean-Christophe Loison3
1Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, 91405 Orsay, France.
Abstract:
Reactive intermediates such as aryl cations play crucial roles in organic and astrochemical processes, yet their characterization remains a significant experimental challenge. The present study offers the first partially vibrationally resolved photoelectron spectrum of the phenyl radical (C6H5), focusing on ionization thresholds to the lowest singlet and triplet states of its cation. Using synchrotron-based photoelectron spectroscopy, we directly determine the adiabatic ionization energy of the first triplet state of phenylium (C6H5+, IEad(ã+ ← X̃) = 9.300(10) eV), and use this as an anchor to derive the singlet-triplet energy gap (ΔE(S-T) = 1.043(32) eV) with assistance from advanced quantum chemical computations. These findings provide new constraints to thermochemical properties essential in arylium ground state determination (and thus essential for a better understanding of arylium chemistry), and establish a framework for future joint spectroscopic-computational studies of more complex arylium compounds.
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