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Vibrational spectra of indole and assignments on the basis of ab initio force fields
Author(s) -
Majoube M.,
Vergoten G.
Publication year - 1992
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/jrs.1250230803
Subject(s) - raman spectroscopy , chemistry , normal mode , force field (fiction) , deuterium , ab initio , fourier transform , basis set , spectral line , molecular physics , indole test , ab initio quantum chemistry methods , normal coordinates , computational chemistry , basis (linear algebra) , molecular vibration , atomic physics , vibration , molecule , geometry , physics , density functional theory , optics , stereochemistry , quantum mechanics , mathematics , organic chemistry
New high‐resolution Fourier transform spectra for indole vapour and its N ‐deuterated analogue and Fourier transform Raman spectra for solid indole are reported. Observed frequencies for normal modes are compared with those calculated from normal coordinate analyses carried out on the basis of ab initio force fields. The latter were calculated using the 3–21G basis set and either the theoretical optimized geometry or that given by microwave spectroscopy. The force field obtained with the optimized geometry was shown to provide and excellent approach for calculating not only frequencies but also IR and Raman intensities. Except for the NH and CH stretching modes, only one scale factor for all the in‐plane modes and another for all the out‐of‐plane modes are needed in order to bring closer the calculated and observed frequencies for indole and for eleven deuterated analogues. Assignments for each normal mode were obtained from potential energy distributions among internal coordinates. Those for normal modes corresponding, in particular, to bands observed also for the tryptophar residue are discussed in detail.