FAR-INFRARED SPECTRUM AND RING-PUCKERING POTENTIAL OF 1,4-DIOXADIENE

Abstract

The far infrared spectrum of gaseous 1,4-dioxacyclohexadiene-2,5, a planar ring molecule isoelectronic with 1,4-cyclohexadiene, has been measured in the range $230-28 cm^{-1}$. A progression of ten Q-branches decreasing in intensity towards higher frequency was found. The eigenvalues inferred from the spectrum were fitted with a mean deviation of about $\pm$ $0.68 cm^{-1}$ to a single-minimum one-dimensional potential function of the form $V(Z) = A(Z^{4} + BZ^{2})$ where Z is a dimensionless ring-puckering coordinate ($b_{lu}$ symmetry), $A = 20.25 cm^{-1}$ and B = 1.255. An attempt to improve the fit was made by expressing the reduced mass as a function of the dihedral angle of puckering and thereby introducing additional kinetic-energy terms in the Hamiltonian. This procedure improved the fit only moderately.