First high-resolution analysis of the ν₂+ν₆ band of the C₂H₂D₂-cis isotopologue of ethylene

The high–resolution infrared spectrum of C₂H₂D₂-cis was recorded for the first time and analyzed in the region of 2400–2700 cm⁻¹, where the ν₂+ν₆ band is located. 1987 transitions were assigned to the ν₂+ν₆ band and 623 ro–vibrational energies of the (v₂=v₆=1) vibrational state were determined from the assigned transitions. Parameters of the effective Hamiltonian were determined from the weighted fit, which takes into account the studied (v₂=v₆=1) vibrational state and six other closely located (but experimentally here not visible) vibrational states of C₂H₂D₂-cis. The obtained “experimental” energy values were used as initial information in the fit. Determined from the fit, a set of 95 parameters reproduces 623 initial energy values of the (v₂=v₆=1) vibrational state, representing 1987 line positions of the ν₂+ν₆ band with the d_rms=3.98×10⁻³ cm⁻¹.