Infrared gas phase intensity measurements, polar tensors, and effective charges of cis-difluoroethylene and its deuterated modifications

All gas phase fundamental vibrational intensities for cis-difluoroethylene and its deuterated modifications have been measured. Isotopic invariance, G sum rule, and quantum chemical information have been used in selecting preferred experimental values for the dipole moment derivatives and polar tensor elements of cis-C2H2F2 and C2D2F2. The G sum rule has been used to determine individual intensity values for the ν11, ν12, overlapped band system of the dihydrogen molecule. Values of the polar tensor elements for cis-difluoroethylene are compared with those found previously for vinylidene fluorine. The hydrogen effective charge value of 0.17 e of cis-difluoroethylene is much smaller than the value of 0.29 e for vinylidene fluoride. The polar tensor of cis-difluoroethylene is shown to provide an excellent estimate of the vibrational intensities of trans-difluoroethylene.