PARTIAL STRUCTURE FOR TRANS-1,2-DIFLUOROETHYLENE FROM HIGH-RESOLUTION INFRARED-SPECTROSCOPY

Three bands in the high-resolution infrared spectrum of trans-1,2-difluoroethylene have been examined. An A-type band at 1274 cm-1 due to in-plane CH bending, nu(10)(b(u)), and a C-type band at 874 cm-1 due to out-of-plane CH bending, nu(6)(a(u)), have been fully analyzed. The B-type component of a hybrid A/B-band at 1657 cm-1 due to the nu(6)(a(u)) + nu(8)(b(g)) combination tone has been partly analyzed. Ground-state rotational constants of A = 1.893 409 7 (24) cm-1, B = 0.134 537 56 (64) cm-1, and C = 0.125 543 44 (59) cm-1 in a Watson-type Hamiltonian have been fit to 1670 ground-state combination differences derived from the three bands. When CH and CC geometric parameters are held at the cis isomer values, a CCF bond angle of 119.6-degrees and a CF bond length of 1.345 angstrom are fit to the principal moments of inertia of the trans isomer. The CCF bond angle is 2.5-degrees smaller and the CF bond length is 0.010 angstrom longer in the trans isomer. A complete structure for the trans isomer awaits analysis of the spectra of the d2 and d1 isotopomers.