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Consistent assignment of the vibrations of symmetric and asymmetric meta-disubstituted benzenes

Kemp, David J.; Tuttle, William D.; Jones, Florence M.S.; Gardner, Adrian M.; Andrejeva, Anna; Wakefield, Jonathan C.A.; Wright, Timothy G.


David J. Kemp

William D. Tuttle

Florence M.S. Jones

Adrian M. Gardner

Anna Andrejeva

Jonathan C.A. Wakefield

Timothy G. Wright


The assignment of vibrational structure in spectra gives valuable insights into geometric and electronic structure changes upon electronic excitation or ionization; particularly when such information is available for families of molecules. We give a description of the phenyl-ring-localized vibrational modes of the ground (S0) electronic states of sets of meta-disubstituted benzene molecules including both symmetrically- and asymmetrically substituted cases. As in our earlier work on monosubstituted benzenes [A. M. Gardner and T. G. Wright. J. Chem. Phys. 135 (2011) 114305], para-disubstituted benzenes [A. Andrejeva, A. M. Gardner, W. D. Tuttle, and T. G. Wright, J. Molec. Spectrosc. 321 (2016) 28], and ortho-disubstituted benzenes [W. D. Tuttle, A. M. Gardner, A. Andrejeva, D. J. Kemp, J. C. A.Wakefield and T. G. Wright, J. Molec. Spectrosc. 344 (2018) 46], we conclude that the use of the commonly-used Wilson or Varsányi mode labels, which are based on the vibrational motions of benzene itself, is misleading and ambiguous. Instead, we label the phenyl-ring-localized modes consistently based upon the Mulliken (Herzberg) method for the modes of meta- difluorobenzene (mDFB) under Cs symmetry, since we wish the labelling scheme to cover both symmetrically- and asymmetrically-substituted molecules. By studying the vibrational wavenumbers obtained from the same force-field while varying the mass of the substituent, we are able to follow the evolving modes across a wide range of molecules and hence provide consistent assignments. We assign the vibrations of the following sets of molecules: the symmetric metadihalobenzenes, meta-xylene and resorcinol (meta-dihydroxybenzene); and the asymmetric meta-dihalobenzenes, meta-halotoluenes, meta-halophenols and meta-cresol. In the symmetrically-substituted species, we find two pairs of in-phase and out-of-phase carbon substituent stretches, and this motion persists in asymmetrically-substituted molecules for heavier substituents; however, when at least one of the substituents is light, then we find that these evolve into localized carbon-substituent stretches.


Kemp, D. J., Tuttle, W. D., Jones, F. M., Gardner, A. M., Andrejeva, A., Wakefield, J. C., & Wright, T. G. (in press). Consistent assignment of the vibrations of symmetric and asymmetric meta-disubstituted benzenes. Journal of Molecular Spectroscopy, 346,

Journal Article Type Article
Acceptance Date Feb 13, 2018
Online Publication Date Feb 15, 2018
Deposit Date Feb 19, 2018
Publicly Available Date Feb 16, 2019
Journal Journal of Molecular Spectroscopy
Print ISSN 0022-2852
Electronic ISSN 0022-2852
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 346
Keywords Vibrations; Frequencies; Ground electronic state; meta-Disubstituted Benzenes
Public URL
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