Rovibrational analysis of the ethylene isotopologue 13C2D4 by high-resolution Fourier transform infrared spectroscopy

Abstract The Fourier transform infrared (FTIR) spectrum of the unperturbed a -type ν 12 band of 13 C 2 D 4 was recorded at an unapodized resolution of 0.0063 cm −1 between 1000 and 1140 cm −1 for a rovibrational analysis. By assigning and fitting a total of 2068 infrared transitions using a Watson’s A -reduced and S -reduced Hamiltonians in the I r representation, rovibrational constants for the upper state ( ν 12  = 1) up to five quartic centrifugal distortion terms were derived for the first time. The root-mean-square (rms) deviation of the fits was 0.00034 cm −1 both in the A -reduction and S -reduction Hamiltonian. The ground state rovibrational constants of 13 C 2 D 4 in the A -reduced and S -reduced Hamiltonians were also determined for the first time by a fit of 985 combination-differences from the present infrared measurements, with rms deviation of 0.00036 cm −1 . The ν 12 band centre of 13 C 2 D 4 was at 1069.970824(17) cm −1 and at 1069.970799(17) cm −1 for the A -reduced and S -reduced Hamiltonians respectively. The ground state constants of 13 C 2 D 4 from this experimental work are in close agreement to those derived from theoretical calculations using the B3LYP/cc-pVTZ, MP2/cc-pVTZ, and CSSD(T)/cc-pVTZ levels of theory.