THE CENTIMETER AND MILLIMETER MICROWAVE-SPECTRUM OF CYCLOBUTANONE

The rotational spectra of cyclobutanone in the ground and the first seven excited states of the ring-puckering vibration, ν27, have been measured in the frequency range 18-250 GHz. The spectra of the ring-puckering excited states with v27 = 8, 9, and 10 and of 11 vibrational excited states belonging to ring-puckering progressions based on the first excited states of the out-of-plane, ν26, and in-plane, ν20, carbonyl bending vibrations have been measured in the frequency range 18-50 GHz. The dependence of the rotational and centrifugal distortion constants on the ring-puckering quantum number has been analyzed in terms of two different reduced ring-puckering potential functions: a mixed quadratic-quartic function and a harmonic oscillator perturbed by a quartic and a Gaussian term. This analysis shows that a one-dimensional model for the ring-puckering is only adequate to describe the features of the low energy levels of this vibration. © 1992.