High resolution FTIR spectrum and analysis of the ν4 band of trans-d2-ethylene (trans-C2H2D2)

The ν4 band of trans-d2-ethylene (trans-C2H2D2) has been recorded with an unapodized resolution of 0.0063 cm−1 in the frequency range of 870–1100 cm−1 by Fourier transform infrared (FTIR) spectroscopy using a Bruker IFS 125R spectrometer. In the analysis of the band, no indications for perturbation were found. By fitting a total of 2121 infrared transitions of ν4 with a standard deviation of 0.00058 cm−1 using a Watson’s A-reduced Hamiltonian in the Ir representation, a set of accurate rovibrational constants up to four sextic terms for the v4 = 1 state was derived. The ν4 band is a C type with a band centre at 987.753336 ± 0.000039 cm−1.