Calculation of the vibrational spectra of pyridine betaine

The vibrational spectra of pyridine betaine and partially deuterated pyridine betaine were calculated and compared with the experimental data. All measured bands in the infrared and Raman spectra were interpreted in terms of normal vibrational modes calculated with the ab initio; SCF/6-31G(d,p) and semi-empirical PM3 methods. The r.m.s. deviations between experimental and calculated SCF frequencies (with a single scaling factor) were 16 cm(-1) for the pyridine ring and 34 cm(-1) for all the vibrational modes. The unsealed frequencies determined with the PM3 method result in r.m.s. deviation over twice as large. The computed band intensities agree qualitatively with the experimental data.