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

Abstract The high–resolution infrared spectrum of C 2 H 2 D 2 - cis was recorded for the first time and analyzed in the region of 2400–2700 cm − 1 , where the ν 2 + ν 6 band is located. 1987 transitions were assigned to the ν 2 + ν 6 band and 623 ro–vibrational energies of the ( v 2 = v 6 = 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 ( v 2 = v 6 = 1 ) vibrational state and six other closely located (but experimentally here not visible) vibrational states of C 2 H 2 D 2 - 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 ( v 2 = v 6 = 1 ) vibrational state, representing 1987 line positions of the ν 2 + ν 6 band with the d rms = 3.98 × 10 − 3  cm − 1 .