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Infrared, Raman and resonance Raman investigations of methylviologen and its radical cation
Author(s) -
Forster M.,
Girling R. B.,
Hester R. E.
Publication year - 1982
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.1250120107
Subject(s) - raman spectroscopy , chemistry , resonance (particle physics) , chromophore , dication , raman scattering , infrared , excitation , analytical chemistry (journal) , radical ion , overtone , photochemistry , spectral line , atomic physics , molecule , optics , ion , physics , electrical engineering , organic chemistry , chromatography , astronomy , engineering
The infrared and Raman spectra of methylviologen (1,1′‐dimethyl‐4,4′‐bipyridine dication, MV 2+ ) have been measured from both the solid dichloride and aqueous solutions. The preresonance behaviour of MV 2+ Raman bands showed that the absorption at ˜196 nm is mainly responsible for the resonance scattering process in MV 2+ . In the region below 1700 cm −1 , nine polarized ( p ˜1/3) resonance Raman bands of the methylviologen radical cation, MV + , were assigned to in‐plane ring modes. Arguments are given that the chromophore of MV + may also partially include the methyl groups. The excitation profiles of the MV + fundamentals, measured with laser wavelengths covering the range 350.6–676.4 nm, reveal three main groups of modes, each behaving differently for the excitation in this range. Modes containing largely ν(CC) ring contributions are mainly coupled with electronic transitions at ˜395, ˜605 and ˜720 nm and yield simple excitation profiles. Modes involving principally the vibrations of the N + CH 3 group show complicated interference peaks in the whole range of the excitation profiles. γ(CCC) is mainly coupled with the absorption at ˜620 nm. Resonance Raman bands of the (MV + ) 2 dimer have been characterized through studies of the concentration dependence of the spectra.