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Ab initio and density functional study of the resonance Raman spectra of Methyl Red, Ethyl Red and their protonated derivatives
Author(s) -
Bell Stephen,
Bisset Alison,
Dines Trevor J.
Publication year - 1998
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(199806)29:6<447::aid-jrs265>3.0.co;2-r
Subject(s) - chemistry , raman spectroscopy , ab initio , protonation , resonance (particle physics) , spectral line , ab initio quantum chemistry methods , density functional theory , computational chemistry , molecule , atomic physics , organic chemistry , physics , ion , optics , astronomy
Resonance Raman (RR) spectra of the acid–base indicators Methyl Red and Ethyl Red and their monoprotonated derivatives were recorded using excitation in the region of their lowest energy electronic absorption bands. The molecular geometries and vibrational spectra of Methyl Red and its protonated derivative were calculated using ab initio (HF/3–21G) and density functional (B3‐LYP/3–21G) methods. Force constants and potential energy distributions were determined from the calculated spectra, after appropriate scaling. Comparison of the RR spectra with the calculated Raman band positions enabled precise vibrational band assignments to be made. The RR spectra provide clear evidence for the structural and electronic changes that accompany protonation. © 1998 John Wiley & Sons, Ltd.