MICROWAVE SPECTRUM AND CONFORMATION OF CIS-1, 2-DIFLUOROETHYLENE OZONIDE (FCHOOFCHO)

Abstract

The microwave spectrum of cis-difluoroethylene ozonide (cis-3, 5-difluoro-1, 2, 4-trioxolane) has been investigated by RF-microwave double resonance in the region of 26.5 - 40.0 GHz. The spectrum consists of two interwoven sets of transitions of similar intensity, arising from two vibrational states of the molecule. The predominant features of the DR spectra are several series of $\mu_{b}$ Q-branch pairs (pumped by $\mu_{c} RF$ transitions), with very few R-branch lines seen. The rotational constants of one state are A = 4256.9, B = 2923.7, and C = 2347.4, giving (A-C) = 1909.5 and k = -D.396. For the other state only Q-branch transitions have been assigned, giving (A-C)-1953.1 and $\kappa = -0.428$. The effects of centrifugal distortion are moderate, being < 150 MHz for the $J = 30 \leftarrow 30$ transitions. These results are consistent with a structure having axial fluorines, and with a ring conformation intermediate between a C-envelope and an $O_{ether}-C$ twist. Bond moment calculations suggest that $\mu_{c} > \mu_{b} > \mu_{a}$, in agreement with the observed spectrum. The presence of two states with intense spectra suggests that the first excited vibrational state is low compared with the $100-200 cm^{-1}$ range seen for other ozonides.