Overtone Investigation of Methyl-Substituted Pyridines

摘要

Conventional near-infrared absorption spectroscopy and intracavity laser photoacoustic spectroscopy have been used to record the room temperature vapor phase overtone spectra of 4-methylpyridine-d_0, 3-methyl-pyridine-d_0, and 2-methylpyridine-d_0 in the #DELTA#v_(CH) = 2-6 regions. These methods are also used to record the hydrogen impurity spectra of 4-methylpyridine-d_7 and 3-methylpyridine-d_7 in the #DELTA#v_(CH) = 2-5 regions. Oscillator strengths are calculated using an anharmonic oscillator local mode model and ab initio dipole moment functions. Ab initio geometries and intensity calculations, which contain no adjustable parameters, are used to assign spectral peaks in the aryl regions. Peaks corresponding to two nonequivalent aryl local modes are assigned in the spectrum of 4-methylpyridine. Peaks corresponding to four nonequivalent aryl local modes are assigned in the spectra of 3-methylpyridine and 2-methylpyridine. The effects of a change in barrier type and size to internal methyl rotation on the complicated methyl band profile are examined. The aryl regions of the hydrogen impurity spectra are similar to the undeuterated compounds, but a significant change is observed in the methyl regions.