Dynamic atomic intensity contributions to fundamental infrared intensities are defined as the scalar products of dipole moment derivative vectors for atomic displacements and the total dipole derivative vector of the normal mode. Intensities of functional group vibrations of the fluorochloromethanes can be estimated within 6.5 km mol(-1) by displacing only the functional group atoms rather than all the atoms in the molecules. The asymmetric CF2 stretching intensity, calculated to be 126.5 km mol(-1) higher than the symmetric one, is accounted for by an 81.7 km mol(-1) difference owing to the carbon atom displacement and 40.6 km mol(-1) for both fluorine displacements. Within the Quantum Theory of Atoms in Molecules (QTAIM) model differences in atomic polarizations are found to be the most important for explaining the difference in these carbon dynamic intensity contributions. Carbon atom displacements almost completely account for the differences in the symmetric and asymmetric CCl2 stretching intensities of dichloromethane, 103.9 of the total calculated value of 105.2 km mol(-1). Contrary to that found for the CF2 vibrations intramolecular charge transfer provoked by the carbon atom displacement almost exclusively explains this difference. The very similar intensity values of the symmetric and asymmetric CH2 stretching intensities in CH2F2 arise from nearly equal carbon and hydrogen atom contributions for these vibrations. All atomic contributions to the intensities for these vibrations in CH2Cl2 are very small. Sums of dynamic contributions of the individual intensities for all vibrational modes of the molecule are shown to be equal to mass weighted atomic effective charges that can be determined from atomic polar tensors evaluated from experimental infrared intensities and frequencies. Dynamic contributions for individual intensities can also be determined solely from experimental data.

No abstract

Padé approximants have long been used to predict virial series coefficients and to provide equations of state for low and high density materials. However, some justified criticism has appeared about this procedure. Although we agree to impose several restrictions on the use of Padé approximants, we indicate that the Padé approximant is still an excellent way to predict the first unknown virial series coefficients. As an example, we report a calculation of the B11=128.6 and B12=155 virial coefficients of the three dimensional hard sphere model that are in excellent agreement with the two most recent estimates. We also consider that the commonly used method to choose among Padé approximants is not completely reliable for this specific application and suggest an alternative new method.

No abstract

Infrared gas phase intensity measurements, polar tensors, and effective charges of cisdifluoroethylene and its deuterated modifications J. Chem. Phys. 78, 7029 (1983); 10.1063/1.444746Infrared gas phase intensity measurements, polar tensors, and effective charges of vinylidene fluoride and its deuterated modificationsThe gas phase fundamental intensities of cis -dichloroethylene and its dideuterated modification have been measured. Isotopic invariance, the G sum rule and the results of molecular orbital calculations have been used to select preferred experimental values for the dipole moment derivatives and polar tensor elements of these molecules. The F sum rule has been used to determine individual intensity values of the v" v 12 overlapped band system of the dihydrogen molecule. Values of the polar tensor elements for cis dichloroethylene are compared with those previously determined for cis-difluoroethylene. The hydrogen effective charge values in these molecules are essentially identical (0.17 and O.l8e). The polar tensor of cis-dichloroethylene is used to predict the vibrational intensities of trans-dichloroethylene.

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.

No abstract

Infrared gas phase intensity measurements. Polar tensors and effective charges of cisdichloroethylened 0 and d 2 Infrared gas phase intensity measurements, polar tensors, and effective charges of vinylidene fluoride and its deuterated modificationsThe experimental polar tensors and effective charges for the X 2 CY molecules where X=F,CI and Y =O,S have been calculated. The polar tensors, with the exception of 3Px/iJxy, and the effective charges of anyone of these molecules can be calculated from these values for the other three molecules. The effective charges of carbon, oxygen, and sulfur are not transferable although those for fluorine and chlorine are transferable within the calculated experimental errors. The effective charge values appear to show trends which reflect the electronegativities of the atoms in the molecules. The sums of the gas phase infrared fundamental intensities of these molecules are shown to be interrelated.