Diode laser spectrum and rovibrational analysis of the nu 10 band of cis-1,2-difluoroethylene

The infrared spectrum of cis-CHF=CHF has been investigated in the ν10 band region between 1100 and 1152 cm-1, at a resolution of 0·002 cm-1, employing a tunable diode laser spectrometer. This vibration of symmetry species B1 yields a strong a-type band, the analysis of which led to the assignment of more than 2000 lines with J⩽67 and K a⩽26. The P- and R-a branch spectrum with high J value is dominated by bandheads spaced by 2C and consisting of a series of lines arising from oblate-type near-degeneracy. From a simultaneous fit of the present GSCD, together with a few literature microwave data, a set of ground state constants up to the quartic coefficients has been obtained using Watson's A-reduction Hamiltonian in the I r representation. A least-squares fit of the assigned transitions provided excited state constants of the ν10 band, which turned out to be free from perturbations.