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The electronic absorption spectra and Raman spectra of pyridine and pyridine-d5 were measured. The vibrational analysis of the nπ* absorption spectrum and the preresonance Raman effect showed that the CH out-of-plane bending vibration ν10a(a2) (of the ground and excited-state frequencies 886 and 331 cm−1 for pyridine) is responsible for the vibronic coupling between the lowest nπ* state and the second lowest ππ* state.
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Mochizuki et al. (1976) studied this question.
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