Rovibrational constants of the ground and v12=1 states of C2D4 by high-resolution synchrotron FTIR spectroscopy

The Fourier transform infrared (FTIR) absorption spectrum of the v(12) fundamental band of ethylene-d(4) (C2D4) was recorded in the 1000-1150 cm(-1) region with a resolution of 0.00096 cm(-1) using the THz/ far-infrared beamline of the Australian Synchrotron. Upper state (v(12) = 1) rovibrational constants consisting of three rotational constants and up to five quartic constants were improved by assigning and fitting 3950 rovibrational transitions using Watson's A-reduced and S-reduced Hamiltonians in the I-T representation. The band centres of the unperturbed A-type v(12) band are found to be 1076.984958(14) cm(-1) and 1076.984813(14) cm(-1) for A-reduced and S-reduced Hamiltonians respectively. The present analysis, covering a wider wavenumber range and higher J and K-c values (up to 58) than previous studies, yielded upper state constants including the band centre which are more accurate than previously reported. The rms deviation of the upper state (v(12) = 1) fit is 0.00040 cm(-1) in the A-reduction and 0.06041 cm(-1) in the S-reduction. Improved ground state rovibrational constants were also determined from the fit of 3151 ground state combination differences (GSCD) from the presently-assigned transitions of the v(12) band of C2D4 using Watson's A-reduced and S-reduced Hamiltonians in the I-r representation. The rms deviation of the GSCD fit is 0.00036 cm(-1) in the A-reduction and 0.00035 cm(-1) in the S-reduction. The ground state constants of C2D4 derived from the experimental GSCD fit are in good agreement with those from theoretical calculations using the B3LYP/cc-pVTZ, MP2/cc-pVTZ, and CSSD/cc-pVTZ levels, up to five quartic constants. (C) 2014 Elsevier Inc. All rights reserved.