High-resolution FTIR spectroscopy of the C-Cl stretching mode of vinyl chloride

The vibration-rotation spectra of natural CH2=CHCl and mono-isotopic CH2=(C HCl)-Cl-37 (isotopic purity, 95%) have been studied in the vp band region n ear 720 cm(-1) with a resolution of 0.005 cm(-1), by using a Fourier transf orm infrared spectrometer. This vibration of symmetry species A' is expecte d to give rise to an a/b hybrid band with a predominant contribution of the a-type component. Both J and K structures have been resolved in different subbranches and the rovibrational analysis led to the assignment of about 3 300 (J less than or equal to 78, K-a less than or equal to 16) and more tha n 3000 (J less than or equal to 79, K-a less than or equal to 16) transitio ns of Cl-35 and Cl-37 isotopomers, respectively. The P- and R-branch spectr um with high J values shows a series of lines arising from oblate-type near -degeneracy. Using Watson's A-reduction Hamiltonian in the I-r representati on, a least-squares fit of the identified transitions provided excited stat e constants of the v(8) band for both the isotopic species, which turned ou t to be free from perturbations.