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A new way of analyzing vibrational spectra. II. Comparison of internal mode frequencies
Author(s) -
Konkoli Zoran,
Larsson J. Andreas,
Cremer Dieter
Publication year - 1998
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1998)67:1<11::aid-qua2>3.0.co;2-1
Subject(s) - isotopomers , adiabatic process , dication , chemistry , molecular vibration , normal mode , atomic physics , spectral line , molecule , molecular physics , physics , quantum mechanics , vibration , organic chemistry
Adiabatic internal frequencies are compared with c ‐vector frequencies and intrinsic frequencies. It is shown that c ‐vector modes are not suitable to characterize molecular fragments ϕ n since they are not localized in ϕ n and their definition leads to unreasonable frequency values. Intrinsic frequencies suffer from a strong dependence on the set of internal parameters chosen to describe the geometry of the molecule. Apart from this, they represent averaged frequencies, for which mass effects and electronic effects are not properly separated. Adiabatic frequencies are based on a dynamic principle, separate properly mass effects and electronic effects and do not depend in any way on the set of internal parameters. This is shown for HF/6‐31G( d , p ) vibrational frequencies of ethene, dichloroethene, benzene, the cyclooctatetraene dication, benzocyclobutadiene, and some of their isotopomers. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67 : 11–27, 1998