The hybrid A/B type ν12 band of trans-ethylene-1,2-d2 by high-resolution Fourier transform infrared spectroscopy

Abstract The FTIR absorption spectrum of the hybrid A / B type ν 12 band of trans- ethylene - 1,2 -d 2 ( trans -C 2 H 2 D 2 ) centered at 1298.038145(19) cm −1 in the 1220–1420 cm −1 region was recorded at an unapodized resolution of 0.0063 cm −1 . Using Watson’s A -reduced Hamiltonian in the I r representation, a total of 2892 a - and b- type transitions was assigned and fitted to upper state ( ν 12  = 1) rovibrational constants up to three sextic terms. The b -type feature of the band was analyzed for the first time. The root-mean-square deviation of the upper state ν 12  = 1 fit was 0.00037 cm −1 while the accuracy of the measurements of the line frequencies was limited to ±0.00065 cm −1 . A set of ground state rovibrational constants up to three sextic terms was also derived from the simultaneous fit of 4597 ground state combination differences from the present analysis and those of the ν 4  +  ν 8 and ν 4 bands of trans -C 2 H 2 D 2 with a root-mean-square deviation of 0.00039 cm −1 . The transition dipole moment ratio μ a μ b of the ν 12 band of trans -C 2 H 2 D 2 was found to be 5.0 ± 0.3.