High-resolution rovibrational analysis of the v(4) band of cis-1,2-difluoroethylene

The diode laser spectrum of cis-1,2-CHF=CHF has been measured and analyzed in the v(4) fundamental region near 1016 cm(-1). This vibration of symmetry species A(1) corresponds to the C-F symmetric stretching motion and gives rise to a strong b-type band. The rovibrational analysis, extended to the P , Q, and R branches, led to the identification of 2800 lines with J less th an or equal to 62, K-a less than or equal to 18, K-c less than or equal to 62. The assigned transitions free of major resonance contributions, fitted using Watson's A-reduction Hamiltonian in the I-r representation, yielded a set of spectroscopic parameters up to the quartic coefficients for the v(4 ) = 1 state. Several perturbation effects occur throughout the band, mainly caused by the first-order c-type Coriolis interaction with the v(5) + v(11 ) vibrational state. Even though no transitions to the perturbing level wer e observed, the band orign and the rotational constants for the perturber w ere determined from a dyad model which includes the Coriolis interaction te rm. (C) 2000 Elsevier Science B.V. All rights reserved.