RING-PUCKERING POTENTIAL FUNCTIONS OF SOME OXYGEN- CONTAINING MOLECULES.

This work was supported by the National Science Foundation.Author Institution: Spectroscopy Laboratory, Massachusetts Institute of Technology, CambridgeThe far-infrared absorption spectra of gaseous cyclopentene oxide, 2-methyl-4,5-dihydrofuran and cyclopentanone have been observed in the range $250-25 cm^{-1}$. The oxygen atom in cyclo-pentene oxide introduces asymmetry into the potential function for inversion of the five-membered ring. The eigenvalues of the inversion vibration can be inferred from the spectra and fitted to a potential function of the form $V(x) = ax^{4}-bx^{2}+cx^{3}$, in which x is the ring-inversion coordinate. The absorption of 2-methyl-4,5-dihydrofuran is complicated by several low-frequency modes but the spectrum can be fairly well interpreted with a double-minimum potential function of the form $V(x) = ax^{4}-bx^{2}$ with a barrier height of $98 cm^{-1}$. Seven sharp Q branches were observed for cyclopentanone which were fitted to a hindered pseudorotational potential function of the form $V=V_{2}(1-\cos 2\phi)/2+V_{4}(1-\cos 4\phi)/2$. The values of $V_{2}$ and $V_{4}$ are respectively 1303 and $29 cm^{-1}$