Improved rovibrational constants for the v7=1 state of ethylene-cis-1,2-d2 (cis-C2H2D2) by high-resolution synchrotron FTIR spectroscopy

Using the far-infrared beamline of the Australian Synchrotron, the spectrum of the v(7) band of ethylene cis-1,2-d(2) (cis-C2H2D2) was recorded in the 640-990 cm(-1) region at an unapodized resolution of 0.00096 cm(-1). A rovibrational analysis of a total of 2823 infrared transitions of the v(7) band was carried out using an asymmetric rotor fitting program based on the Watson's A-reduced Hamiltonian in the I-r representation to derive up to four sextic constants with a rms deviation of 0.00035 cm(-1). From the fitting of 2634 ground state combination differences (GSCDs) of cis-C2H2D2 which were derived from the infrared transitions of the v(7) band of this work, and v(10) and v(12) bands of previous studies, together with 22 microwave frequencies, accurate ground state constants of cis-C2H2D2 up to four sextic terms were obtained. The rotational constants (A, B, and C) of the v(7) = 1 state of cis-C2H2D2 were found to agree within 0.5% with the calculated values using B3LYP/cc-pVTZ and MP2/cc-pVTZ levels of theory. From this work, the band center of v(7) at 842.209489(20) cm(-1) and the rovibrational constants of the v(7) = 1 state of cis-C2H2D2 were determined with better accuracy than previously reported. (C) 2016 Published by Elsevier Inc.