Adalberto Bono Maurizio Sacchi Bassi

The polar tensors, effective charges, and infrared intensities of X2CY molecules

The experimental polar tensors and effective charges for the X2CY molecules where X=F,Cl and Y=O,S have been calculated. The polar tensors, with the exception of ∂px/∂xy, and the effective charges of any one 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.

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.

Infrared gas phase intensity measurements, polar tensors, and effective charges of vinylidene fluoride and its deuterated modifications

All gas phase fundamental vibrational intensities for vinylidene fluoride 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 these molecules. The values of these intensity parameters are compared with those found for other molecules. The experimental values are interpreted in terms of electronic charge distortions occurring in these molecules for the various vibrations.

Infrared gas phase intensity measurements. Polar tensors and effective charges of cis‐dichloroethylene‐d0 and d2

The 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 ν4, ν12 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 0.18e). The polar tensor of cis‐dichloroethylene is used to predict the vibrational intensities of trans‐dichloroethylene.

On Padé approximants to virial series

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.

The theoretical calculation of polar tensors and dipole moment derivatives: BF3 and Bcl3

The experimental and CNDO polar tensors for BF3 and Bcl3 are reported. To satisfy charge and symmetry restrictions the importance of the calculation of limiting values for theoretical polar tensor elements is demonstrated. A convenient method to transform polar tensor elements to ∂p/∂Qi values is presented. The atomic effective charges, mean dipole moment derivatives, and anisotropies of BF3 and Bcl3 are reported and discussed.

G‐intensity sum rule applications: XY3 molecules

Using the pyramidal XY3 (X=N, P; Y=H, F) molecules as examples, the G‐intensity sum rule of Crawford, expressed in terms of effective charges, is shown to be an effective test of the numerical results of vibrational analyses. Errors in previously reported effective charge values for NF3 and PF3 are corrected. Values for the as yet unreported polar tensors of these molecules are presented. Comparisons of these results with those previously reported for other molecules are made.

The polar tensors, effective charges, and infrared intensities of silane

Symmetry conditions of a partially deuterated silane SiD3H have been used to separate overlapped bands and to determine the correct signs of the dipole moment derivatives for SiH4, SiD4, and SiD3H. These conditions were also able to predict the intensity of the A3′ band of SiD3H. Polar tensor isotopic invariance and the F and G sum rules also played a fundamental role in this work. Separation ratios, polar tensors, and effective charges of the silanes are reported.

A continuum thermodynamical approach to electrochemical systems

This work focuses on formulating constitutive models for the bulk and double layer regions of an electrochemical system based on the fundamentals of modern continuum thermodynamics. Particularly, the constitutive models proposed accounting for transport phenomena in electrochemical systems by emphasizing the possibility of cross-coupling between two or more phenomena. Upon deriving a set of thermodynamic restrictions from the Müller-Liu approach of the second law of thermodynamics and axioms of constitutive theory, non-equilibrium quantities are examined in detail, and constitutive answers of the bulk and double layer regions are discussed. Moreover, the conditions for the thermodynamic equilibrium are evaluated for each region as well as the occurrence of dissipative mechanisms. Besides offering a proper formulation for non-equilibrium electrochemical systems, the approach described in this work can be easily extended to more complex chemical systems.

Dynamic atomic contributions to infrared intensities of fundamental bands

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.