High-resolution FTIR study of the nu(2) fundamental of cis-CHF = CHF

The high-resolution FTIR spectrum at room temperature of cis-1,2-difluoroet hylene has been analyzed in the fundamental region from 1670 to 1760 cm(-1) . This vibration of A(1) symmetry, corresponding to the C=C stretching, giv es rise to a strong b-type band approximately centered at 1719 cm(-1). The rovibrational analysis led to the assignment of many transitions in the P, Q and R branches with J'less than or equal to 70, K'(a) less than or equal to 30, K'(c) less than or equal to 69. From a simultaneous Dt of the ground state combination differences coming from the present work and the previou sly analyzed v(4) and v(10) fundamentals, together with a few literature mi crowave data, a set of ground state parameters, including all the quartic a nd four new sextic centrifugal distortion coefficients, was derived. Using the Watson's A-reduction Hamiltonian in the Ir representation, from the fin al fit of about 3600 assigned transitions, accurate rovibrational constants for the upper state were obtained with a standard deviation of about 8 x 1 0(-4) cm(-1).