COMPLETE VAPOR-PHASE ASSIGNMENT FOR THE FUNDAMENTAL VIBRATIONS OF FURAN, PYRROLE AND THIOPHENE

Vibrational spectroscopic studies, including IR vapor, Raman vapor and Raman liquid spectra, have been made to obtain the complete set of fu ndamental vibrational frequencies in the vapor and liquid states for f uran, pyrrole and thiophene. For furan, vapor values have been determi ned for the two previously ambiguous fundamentals, nu11 and nu18. Also determined is the vapor frequncy of two fundamentals of furan for whi ch only the liquid value had been known. The fundamental vibrational f requencies of pyrrole have been completely determined in the gas and l iquid states. The thiophene results confirm the assignment of Rico et al. [Spectrochim. Acta 21, 689 (1965)], although for several of the fu ndamental modes the vapor frequency is now measured. The Raman vapor s pectra are conclusive concerning the refinements in vibrational assign ment for furan and pyrrole, where virtually every binary combination b and involving the out-of-plane fundamentals that yield an A1 transitio n is observed. The Raman vapor results establish two significant Fermi resonances affecting fundamental vibration levels in pyrrole. Also, C -13 and S-34 isotopomers are identified in the Q-branches of the Raman vapor spectra at natural abundance. A comparison of the spectroscopic and calorimetric ideal-gas thermodynamic properties is made. The diff erences are negligible in the region where the calorimetric data are m ost reliable.