High-resolution infrared study of collisionally cooled trans-1,2-dichloroethylene

A recently constructed long-path enclosive flow cooling apparatus is employed to obtain the Fourier transform gas-phase infrared absorption spectrum of natural isotopic trans-1,2-dichloroethylene with a resolution of 0.00190 cm−1 in the 800-1000 cm−1 spectral region. The rotational structure of the out-of-plane CH flapping fundamental has been analyzed for the isotopic analogues 35Cl2 and 35Cl37Cl using the Watson A-reduced Hamiltonian model and Ir-representation. A ground-state combination difference analysis for the 35Cl37Cl isotopomer based on 1402 assigned transitions belonging to the ν6 band yields a band origin of 897.94493(10) cm−1 and values for the ground-state rotational constants: A0 = 1.7466454(44) cm−1, B0 = 0.05019643(82) cm−1 and C0 = 0.04877977(82) cm−1 together with quartic centrifugal distortion constants. The red-shift of 0.00444(10) cm−1 observed for the ν6 band origin of 35Cl37Cl relative to the 35Cl2 band origin is now consistent with the Rayleigh rule.