Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes
| Autor: | William D. Tuttle, Anna Andrejeva, Adrian M. Gardner, Timothy G. Wright, David J. Kemp, Jonathan C.A. Wakefield, Florence M.S. Jones |
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| Rok vydání: | 2018 |
| Předmět: |
Physics
010304 chemical physics Substituent Electronic structure 010402 general chemistry 01 natural sciences Atomic and Molecular Physics and Optics Spectral line 0104 chemical sciences chemistry.chemical_compound chemistry Ionization Molecular vibration 0103 physical sciences Molecule Physical and Theoretical Chemistry Symmetry (geometry) Atomic physics Spectroscopy Excitation |
| Zdroj: | Journal of Molecular Spectroscopy. 344:46-60 |
| ISSN: | 0022-2852 |
| DOI: | 10.1016/j.jms.2017.10.011 |
| Popis: | 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 Varsanyi 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. |
| Databáze: | OpenAIRE |
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