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

Abstract

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-C,H,F, and C,D,F,. The G sum rule has been used to determine individual intensity values for the VII' V l2 , overlapped band system of the dihydrogen molecule. Values of the polar tensor elements for cisdifluoroethylene 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.

Vibrational and Quantum Chemical Studies of 1,2-Difluoroethylenes: Spectra of 1,2-13C2H2F2 Species, Scaled Force Fields, and Dipole Derivatives

“…We have a slight preference for our choice of in-plane bending coordinates. Except for a change of sign, these resemble those of Pearce and Levin 11 but differ from those of Kagel et al , Compared with the latter, in the d 0 isotopomers ours yield more pure CH bending motions for the frequencies around 1300 cm -1 as well as simpler descriptions of the modes in the 500−800 cm -1 region. Overall, the off-diagonal terms in the potential energy distributions (PED) are smaller with our coordinates than with those used previously. , …”

“…The molecules of cis - and trans -1,2-difluoroethylene have been the subject of a number of experimental − and theoretical studies. − A major interest has been the extent to which parameters of all kindsbond lengths and angles, force constants, and atomic polar tensorsare transferable from one isomer to the other. However, in each of these areas, significant problems remain.…”

Tunable Diode Laser Spectroscopy of cis-1,2-Difluoroethylene: Rovibrational Analysis of the ν9 and ν5+ν10 Bands and Anharmonic Force Field

“…The low-resolution infrared spectra of cis -CHFCHF were examined a long time ago and band centers have been determined for all the fundamentals, some overtones and combination bands. More recently, ab initio calculations of the harmonic force field together with the vibrational frequencies have been carried out and gas-phase fundamental intensities have been measured . The microwave spectrum was investigated much earlier, mainly in relation to the determination of the rotational constants and the dipole moment.…”

A theoretical study of the vibrational spectrum of maleimide

“…As a result, their intensities are generally weak or very weak, as can be seen in Table 2. Another example, the sum of the symmetric and asymmetric CAH stretching intensities in cis-C 2 H 2 F 2 is only 3.5 ± 3.5 km mol À1 [25].…”