Jump to main content
Jump to site search

Issue 6, 2018
Previous Article Next Article

The ortho-benzyne cation is not planar

Author affiliations


A recent review on the photoionisation of the C6H4 isomer ortho-benzyne suggests that bands reported in earlier photoelectron spectra might be due to side products or contaminations, while computations raise doubts, whether the cation has a planar geometry. We therefore reinvestigate the photoionisation of ortho-benzyne, generated by pyrolysis from benzocyclobutenedione, by photoion mass-selected threshold photoelectron (ms-TPE) spectroscopy using synchrotron radiation. The experiments are accompanied by a theoretical study that investigates the structure of the ortho-benzyne cation systematically as a function of the computational method, up to CASPT2(11,14) ab initio computations. Our study leads to a re-evaluation of the ionisation energy of ortho-benzyne. It reveals that the ortho-benzyne cation has indeed a twisted C2 geometry rather than a C2v structure. A vertical ionisation energy IEvert of 9.77 eV and an adiabatic ionisation energy of IEad = 9.56 eV are computed for ortho-benzyne. A Franck–Condon simulation of the photoelectron spectrum based on the CASPT2 results and including three electronic states of the cation is in agreement with the experiment and yields IEad = 9.51 eV (+50 meV/−100 meV). Since this value is in contrast with previous work, the ionisation energy has to be revised based on our study. Computational methods based on density functional theory give a reasonable description of the cationic ground state, but fail for the corresponding excited electronic states that are indispensible for a proper assignment of the photoelectron spectrum.

Graphical abstract: The ortho-benzyne cation is not planar

Back to tab navigation

Supplementary files

Publication details

The article was received on 30 Nov 2017, accepted on 09 Jan 2018 and first published on 09 Jan 2018

Article type: Paper
DOI: 10.1039/C7CP08055G
Citation: Phys. Chem. Chem. Phys., 2018,20, 3988-3996
  •   Request permissions

    The ortho-benzyne cation is not planar

    D. Kaiser, E. Reusch, P. Hemberger, A. Bodi, E. Welz, B. Engels and I. Fischer, Phys. Chem. Chem. Phys., 2018, 20, 3988
    DOI: 10.1039/C7CP08055G

Search articles by author