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Identifying complex Fermi resonances in p-difluorobenzene using zero-electron-kinetic-energy (ZEKE) spectroscopy

Kemp, David J.; Gardner, Adrian M.; Tuttle, William D.; Midgley, Jonathan; Reid, Katharine L.; Wright, Timothy G.


David J. Kemp

Adrian M. Gardner

William D. Tuttle

Jonathan Midgley

Professor of Physical and Theoretical Chemistry


The vibrations of the ground state cation (X ̃2B2g) of para-difluorobenzene (pDFB) have been investigated using zero-electron-kinetic-energy (ZEKE) spectroscopy. A comprehensive set of ZEKE spectra were recorded via different vibrational levels of the S1 state (< 00 + 1300 cm 1). The adiabatic ionization energy (AIE) for pDFB was measured as 73869±5 cm 1. Use of different intermediate levels allows different cationic vibrational activity to be obtained via the modification of the Franck-Condon factors for the ionization step, allowing the wavenumbers of different vibrational levels in the cation to be established. In addition, assignment of the vibrational structure in the ZEKE spectra allowed interrogation of the assignments of the S1  S0 transition put forward by Knight and Kable [A. E. W. Knight and S. H. Kable, J. Chem. Phys. 89, 7139 (1988)]. Assignment of the vibrational structure has been aided by quantum chemical calculations. In this way it was possible to assign seventeen of the thirty vibrational modes of the ground state pDFB+ cation. Evidence for complex Fermi resonances in the S1 state, i.e. those that involve more than two vibrations, was established. One of these was investigated using picosecond time-resolved photoelectron spectroscopy. In addition, we discuss the appearance of several symmetry-forbidden bands in the ZEKE spectra, attributing their appearance to a Rydberg state variation of an intrachannel vibronic coupling mechanism.


Kemp, D. J., Gardner, A. M., Tuttle, W. D., Midgley, J., Reid, K. L., & Wright, T. G. (2018). Identifying complex Fermi resonances in p-difluorobenzene using zero-electron-kinetic-energy (ZEKE) spectroscopy. Journal of Chemical Physics, 149(9), (094301). doi:10.1063/1.5045544. ISSN 0021-9606

Journal Article Type Article
Acceptance Date Aug 16, 2018
Online Publication Date Sep 5, 2018
Publication Date Sep 7, 2018
Deposit Date Sep 6, 2018
Publicly Available Date Sep 6, 2018
Journal The Journal of Chemical Physics
Print ISSN 0021-9606
Electronic ISSN 1089-7690
Publisher AIP Publishing
Peer Reviewed Peer Reviewed
Volume 149
Issue 9
Pages 094301
Keywords Physical and Theoretical Chemistry; General Physics and Astronomy
Publisher URL


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