Raman vapor spectrum and vibrational assignment for pyridine

Assignment modifications for the pyridine fundamentals are proposed, based on first time Raman vapor measurements, and a more complete set of infrared and Raman spectra for the gas and liquid. Raman polarization measurements are newly given for some 70 lines between 1600 and 3000 cm(-1). The Kakiuti et al. (Kakiuti et al., J. Mel. Spectrosc. 61 (1976) 164) assignment for the nonplanar modes in CS2 solution is shown to be the only previous correct assignment. Planar assignment modifications, though generally small, are warranted because of the benchmark nature of pyridine. A previous set of vibrational frequencies, derived from a scaled 4-21G force field calculation (Pongor et al., J. Am. Chem. Sec. 106 (1984) 2765; Pongor et al., J. Mel. Spectrosc. 114 (1985) 445), is in excellent agreement with the observed fundamentals, and in fact, tips the balance in favor of assigning nu(22) to 1053 cm(-1) Ideal-gas entropies derived from spectroscopic constants are also seen to be in excellent agreement with those from calorimetry (Chirico et al., J. Chem. Thermodyn. 28 (1996) 797; Chirico and Steele, J. Chem. Thermodyn. 28 (1996) 819). (C) 1998 Elsevier Science B.V. All rights reserved.