VIBRATIONAL OVERTONE STUDY OF 5-MEMBERED AROMATIC HETEROCYCLES - FERMI RESONANCE INTERACTIONS

The CH stretching overtone spectra of furan and several thiophenes are examined in regions where there is spectral evidence for vibrational state interactions. The interactions appear to behave differently in furan and in the thiophenes. However, in both molecules, the interactions are dominated by distinct resonances rather than by purely statistical interactions with the large density of underlying vibrational states. In thiophene, these distinct resonances give rise to energy shifts and transition intensity redistribution in the spectra. The resonances can be tuned in or tuned out through substitution of the parent molecule. Explanations are advanced for the specific nature of the various interactions.