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Analysis of the Vibrational Spectra of Heterocyclic Aromatic Molecules Showing Internal Proton and Deuterium Transfer
Author(s) -
Pfeiffer M.,
Lenz K.,
Lau A.,
Elsaesser T.,
Steinke T.
Publication year - 1997
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/(sici)1097-4555(199701)28:1<61::aid-jrs81>3.0.co;2-x
Subject(s) - chemistry , deuterium , excited state , raman spectroscopy , wavenumber , spectral line , molecular vibration , molecule , resonance (particle physics) , molecular physics , normal mode , atomic physics , vibration , physics , organic chemistry , optics , quantum mechanics , astronomy
Earlier investigations of the vibrational spectra of three related proton transfer molecules belonging to the hydroxyphenylbenzoazoles were extended to include deuterium shift effects of the transfer hydrogen in the resonance Raman and infrared spectra. Semi‐empirical calculation of the force matrix on the basis of PM3 including the calculation of Raman intensities within the VAMP package gives good quantitative results in the spectral range of the low‐wavenumber in‐plane modes up to 1000 cm ‐1 . For the wavenumber range of the π‐bond stretching modes, scaling must be applied. The strongest deuterium shift effects observed in the spectra are reproduced by the calculation and serve to verify the assignment. In the spectra characteristic combination tone patterns are observed and most of their lines result from combinations with one low‐wavenumber mode for each molecule, representing an in‐plane deformation. This mode is at 469 cm ‐1 for 2‐(2′‐hydroxy‐5′‐methylphenyl)benzotriazole, at 293 cm ‐1 for 2‐(2′‐hydroxyphenyl)benzothiazole and at 310 cm ‐1 for 2‐(2′‐hydroxyphenyl)benzoxazole. These modes show strong anharmonicities in the ground and excited electronic states of the resonance transition. It is suggested that the vibrational coordinates belonging to these modes contribute substantially to the reaction path in the excited electronic state along which the proton transfer proceeds. © 1997 by John Wiley & Sons, Ltd.