VIBRATIONAL OVERTONE SPECTROSCOPY OF PYRIDINE AND RELATED COMPOUNDS

Abstract

Vibrational overtone spectra have been observed for pyridine, fluoro- and chlorosubstituted pyridines, and pyrazole. The overtone spectrum of pyridine consists of a progression of two peaks at each overtone level. Spectra of 3-fluoropyridine and 2,6-difluoropyridine show similar progressions of two peaks. Multiple transitions are also observed in the third overtone CH stretch spectra of 3,4,5-trichloropyridine, 3,5-dichloropyridine, and pyrazole. In earlier local mode $analyses^{1,2}$ of the liquid phase overtone spectrum of pyridine the two peaks were assigned to the $C_{\alpha}-H$ and $C_{\beta, \gamma}-H$ stretches. However, this local mode assignment is not sufficient to explain our results, in particular the observation of two peaks in the third overtone spectrum of 3,4,5-trichloropyridine and four peaks in the third overtone spectrum of 3,5-dichloropyridine.