INFRARED-SPECTRUM AND ROVIBRATIONAL ANALYSIS OF THE NU-6 BAND OF VINYL-CHLORIDE BY DIODE-LASER SPECTROSCOPY

The gas-phase infrared spectrum of natural CH2CHCl has been measured in the ν6 band region near 1281 cm-1 at a resolution of about 0.002 cm-1 using a tunable diode laser spectrometer. This vibration of symmetry species A′ is expected to give rise to an a b hybrid band, which resulted mainly composed by a-type transitions. The spectrum investigated exhibits patterns characteristic of molecules approaching to the prolate symmetric-top limit; the rovibrational analysis in the P, Q, and R branches led to the assignment of more than 1000 lines with J ≤ 40 and Ka ≤ 14. The band was found to be affected by Coriolis-type resonance and the ν9 + ν11 state seems to be involved in the perturbation. From a simultaneous fit of the obtained ground state combination differences, together with microwave data available in the literature, a set of ground state constants up to the quartic coefficients has been determined using the Watson's A-reduction Hamiltonian in the I′ representation. A least-squares fit of the assigned transitions yielded a set of effective constants for the first excited vibrational state of the ν6 of CH2CH 35Cl. © 1992.