New combining rules for well parameters and shapes of the van der Waals potential of mixed rare gas systems

New combining rules are presented for calculating the van der Waals well parametersε andσ as well asC ₆,C ₈ andC ₁₀ for the mixed rare gas systems from the corresponding values of the homogeneous dimers. The combining rules forε andσ are tested by comparison with the recent compilation of Aziz and found to be superior to the best previous combining rules selected by Aziz. Effective Born-Mayer repulsive potential parameters are determined from the model potential of Tang and Toennies and make possible the calculations of accurate potential curves for all combinations of rare gas atoms.     

Dipole moment functions of van der waals complexes of HF and HCl with rare gas atoms

A simple electrostatic model based on a single-centre multipole expansion is applied to derive the dipole moment functions of complexes formed by the HF (DF) and HCl (DCl) molecules with rare gas atoms. Vibrationally averaged ground state dipole moments agree quite well with the available experimental data. Some transition dipole moments for the internal modes of complexes are also estimated.     

Collisional energy-transfer processes involving van der waals bonds

Collisional energy transfer to van der Waals complexes is studied via trajectory calculations. Efficient build-up of energy in the van der Waals bond and its subsequent fragmentation is a result of the flow of energy from translation through the chemically bonded molecular unit. Despite such an efficient energy flow, migration of the vibrational energy initially present in the molecular unit into the van der Waals bond is not important. V-V energy transfer between the excited molecular unit and the incident molecule is very inefficient. O₂ is chosen for the model calculations.     

Nonretarded van der waals interaction between two metal spheres

An approximate solution is found to an equation defining the spectrum of surface plasmons in systems of two equal metal spheres and two plane metal surfaces. The spectrum obtained is then used for calculation of the van der Waals interaction energy between these spheres at large and small separations and between the plane metal surfaces.     

A van der waals theory with quartic density gradients

Functional methods show that biphasic mixtures of rods and solvent have interfacial free energies quartic in the density gradient in contrast to the quadratic van der Waals theory. The result is novel because there is more than one order parameter and because the coupling is via the distribution functions.     

The electronic spectra of argon-tetracene van der waals complexes

A simple relationship is shown to occur between spectral line position and the number of bound argon atoms in the electronic spectrum of argon-tetracene van der Waals molecules, in contrast to the conclusion of other workers. We show that bonding information may be obtained from such spectra.     

Sum-rule moment bounds on long-range van der waals potentials

Quantum-mechanical sum rules and results from the theory of moments are employed in the construction of rigorous bounds on the long range van der Waals interactions of atoms and molecules.     

The anisotropic van der waals potential for He-N2

We have calculated the spherical v₀ and anisotropic radial components v₂ and v₄ in the usual Legendre expansion for the rigid rotor He-N₂ potential using the method of Tang and Toennies Potential curves covering the range of internuclear distances from 2.5 to 8.0 Å, which includes the minimum region, arc presented and compared with a recent experimental potential derived from differential total cross sections.     

The maximum melting temperatures in strain-crystallized van der waals networks

A theory of strain-crystallization of random networks comprised of stereoregular chains is developed. The crosslinks are assumed to be expelled from crystal cores. For this reason, the rubber is considered to be represented as a random eutectoid copolymer, the thermodynamics of strain crystallisation of which is described by the use of the van der Waals model of networks. The strain dependence of the maximum melting temperatures, the degree of crystallinity and the average thickness of the crystallites calculated are shown to be in fair accord with experimental data.Dedicated Prof. Dr. R. Bonart on the occasion of his 60th birthday.     

On the interdependence of van der waals and double layer forces

We study the effect of coupling the electrostatic and low frequency electrodynamic responses of colloidal systems. Exact results are reported for the van der Waals free energy of interaction of non-uniform electrolyte across planar dielectric and planar charged dielectric across non-uniform electrolyte. In both cases, the results depend on the double layer repulsion.     

The use of van der waals molecules to identify spectroscopic origins

A technique for identifying the origin band of an electronic transition is described. The technique utilizes the increased linewidth of helium van der Waals complexes caused by vibrational predissociation when the molecular part of the complex is vibrationally excited. The method is applied to the visible spectrum of chromyl chloride, and we conclude that the d₅ band of chromyl chloride is not a second electronic origin.     

Application of the modified van der waals equation for unsaturated vapour and liquid states

The Law-Lielmezs (L-L) modification of the Van der Waals equation of state: P = RT/(V-b)-a(T)/V² where: a(T) = a(T_c)·a(T_c·a(T¹) and: a(T¹) = 1 + pT^1q has been extended to include unsaturated states in terms of a correcting function C_f(such that the α(T¹) term becomes: a(T¹) = 1 + _pC_fT^1q The proposed extension has been compared with the results obtained by the use of the original Van der Waals equation of state.     

Perylene-naphthalene: restricted IVR in a strongly bound van der waals molecule

The study of the spectroscopic properties of molecular complexes of perylene has been extended to naphthalene. Calculations extrapolated from earlier work predict a deviation from center-of-mass, parallel-plane geometry, and this prediction is supported by the experimental data. The complexes show a very large red-shift, of 748 cm⁻¹, which is almost twice that of benzene. A 2 : 1 complex was also observed, exhibiting a nearly harmonic shift, to 1443 cm⁻¹. The spectra show little perturbation of the in-plane modes from the free perylene case, but strong new low-frequency bands are seen, which may be attributed to complexation-induced deformation of the perylene ground state. The most important result is that strong resonance fluorescence, which was suppressed in small molecule complexes of perylene, is observed for the perylene-naphthalene 353 cm⁻¹in-plane mode. By contrast, excitation into combinations of out-of-plane deformation modes in the same energy region effectively eliminated the resonance fluorescence. This is, therefore, an important case where a mode of a big molecule is decoupled from the quasi-continuum, and develops small-molecule character.     

On the van der waals energy of two half-spaces at small separations

It is shown that the introduction of a cut-off wavenumber corresponding to electron-hole excitations leads to a 10% reduction of the Lifshitz van der Waals attraction of low density metallic half-spaces at small separations.     

Multipoint padé theory and semi-empirical method for the van der waals interactions

In the context of the multipoint Padé theory, the van der Waals coefficients obtained from the semi-empirical method are seen to be lower bounds. With a slightly different constraint, the method also gives upper bounds.     

The generalized van der waals partition function. I. basic theory

Sandler, S.I., 1985. The generalized van der Waals partition function. I. Basic theory. Fluid Phase Equilibria, 19:233-257 In this paper we provide a new derivation of the generalized van der Waals partition function for pure fluids and mixtures, and show how this partition function can be used as a basis for understanding equations of state, their mixing rules, and excess free energy (activity coefficient) models. The results presented here clarify some of the confusion which presently exists in the literature concerning the ramifications of local composition thermodynamic models, and provide the theory for papers to follow which combine the generalized van der Waals partition function and our computer simulation results to obtain new, statistical mechanical-based thermodynamic models.