Vibrations of the p-chlorofluorobenzene cation. Issue 18 (30th April 2018)

• Record Type: Journal Article
• Authors: Kemp, David J.; Whalley, Laura E.; Tuttle, William D.; Gardner, Adrian M.; Speake, Benjamin T.; Wright, Timothy G.
• Is Part Of: Physical chemistry chemical physics. Volume 20:Issue 18(2018)
• Page Start: 12503
• Page End: 12516
• Publication Date: 2018-04-30
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c8cp01274a
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Vibrational wavenumbers are established for twenty modes of the p -chlorofluorbenzene cation and two Fermi resonances are identified in the S1 state. Abstract : The vibrations of the ground state cation (X̃ 2 B1 ) of para -chlorofluorobenzene ( p ClFB) have been investigated using zero-electron-kinetic-energy (ZEKE) spectroscopy. ZEKE spectra were recorded using different vibrational levels of the S1 state as intermediate levels, for which assignments were put forward in an earlier paper [W. D. Tuttle, A. M. Gardner, and T. G. Wright, Chem. Phys. Lett., 2017, 684, 339]. These different intermediate levels dramatically modify the Franck–Condon factors for the ionization step. The adiabatic ionization energy (AIE) for p ClFB was measured as 72 919 ± 5 cm −1, and analysis of the vibrational structure in the ZEKE spectra allowed further interrogation of the assignments of the REMPI spectrum. Assignment of the vibrational structure has been achieved by comparison with corresponding spectra of related molecules, via quantum chemical calculations, and via shifts in bands between the spectra of the 35 Cl and 37 Cl isotopologues. In this way it was possible to assign twenty out of the thirty vibrational modes of the ground state p ClFB + cation. Additionally, evidence for Fermi resonances between some vibrational levels was found in the S1 state, but no large-scale intramolecular vibrational redistribution (IVR) was seen in the spectra here. Finally, we discuss trends in AIE shifts for benzenes with one or two halogen atoms or methyl substituents.