Charge-overlap effects in the non-additive triple-dipole interaction

A formal partial wave analysis of the third-order energy for the interaction of three non-degenerate S-state atoms is used to identify those non-additive terms which, in the limit of negligible charge overlap between the interacting atoms, reduce to the usual long-range expanded form of the triple-dipole energy. Pseudo-state techniques are used to evaluate these terms, both with and without the inclusion of charge-overlap effects, over a range of interatomic separations and angles for the interaction of three ground-state hydrogen atoms. These results are used as a model to discuss the way in which charge-overlap effects modify the usual long-range result for the triple-dipole energy. In addition to the familiar modification of the radial dependence of the interaction energy, charge-overlap effects are found to give rise to a modification of the angular dependence; the latter effect has no analogue in two-atom interactions. The significance of these results is discussed briefly.     

Convergence of the multipole results for first order orientation dependent intermolecular forces using NH3-H+ as a model interaction

The NH₃-H⁺ interaction is used as a model for discussing the usefulness of energy multipole expansions for interactions where the first order energy plays an important role. The multipole results for the first order energy are analysed formally and are compared numerically with the non-expanded first order energy for a variety of NH₃-H⁺ relative configurations. The results are used to discuss the limitations of the multipole expansion of the first order energy which can be very severe for some NH₃-H⁺ collision trajectories.     

On the validity and properties of the atom-atom potential as a function of intermolecular separation,configuration, and partial wave order

The intermolecular partial wave expansion of the atom-atom potential U is reviewed briefly and developed, by using results due to Sack, so that the radial components of the expansion can be evaluated to arbitrary accuracy for all relevant partial wave orders and values of the intermolecular distance r. These results are used to study the convergence of the partial wave expansion of U as a function of partial wave order, r, intermolecular orientation, and the anisotropy of the interacting molecules. In marked contrast to previous work it is found that many of the higher order partial wave components of U are important relative to the isotropic term even for the interaction of relatively spherical molecules and that the results obtained from a truncated partial wave expansion depend significantly upon the method of summation due to the generally poor convergence of the expansion. The validity of the atom-atom potential as a representation of the correct attractive intermolecular potential is also discussed in some detail. There are basic problems associated with the representations furnished by both the isotropic and the anisotropic parts of the atom-atom potential at intermediate and large r. The different convergence properties of the r ^-1 expansions of the partial wave expansions of U and of the correct potential for these values of r is illustrated by using model interactions. While it appears that it may be possible to obtain a qualitatively reasonable representation of the attractive part of an intermolecular potential over a useful range of r from atom-atom results, this apparently cannot be achieved for wider ranges of r or for the purely anisotropic part of the potential.     

On validity of the weak interaction renormalizable theory of Tanikawa-Watanabe

It is shown that the weak interaction renormalizable theory of Tanikawa-Watanabe, which in its simple formulation predicts essential effects in (e^±p) scattering, contradicts the experimental data on elastic scattering of electrons and positrons on protons if the existing concepts on the role of the two-photon exchange in these processes are valid.     

The statistical correlation of intermolecular coriolis and centrifugal forces

Correlation functions are computed in the laboratory frame for the molecular coriolis and centrifugal forces with respect to a frame of reference static in the laboratory. The molecular Coriolis and centrifugal forces in this laboratory frame result from a combination of the molecule's rotational and translational motion, and correlate statistically these two types of motion. They are not usually considered in the theory of decoupled rotational or translational diffusion. Correlation functions are computed for the enantiomers and racemic mixture of liquid bromochlorofluoromethane, and for dichloromethane liquid subjected to a strong, uniaxial, electric field of force in the z axis of the laboratory frame.     

On the contribution of three-body forces to Nd interaction at intermediate energies

Available data on large-angle nucleon-deuteron elastic scattering Nd→dN below the pion threshold give a signal for three-body forces. The problem exists of the separation of possible subtle aspects of these forces from off-shell effects in two-nucleon potentials. By considering the main mechanisms of the process Nd→dN, we show qualitatively that in the quasi-binary reaction N+d→(NN)+N with the final spin singlet nucleon-nucleon pair in the S-state, the relative contribution of the three-nucleon forces differs substantially from the elastic channel. It gives a new testing basis for the problem in question.     

Direct measurement of the intermolecular forces confining a single molecule in an entangled polymer solution

We use optical tweezers to directly measure the intermolecular forces acting on a single polymer imposed by surrounding entangled polymers (115 kbp DNA, 1 mg/ml). A tubelike confining field was measured in accord with the key assumption of reptation models. A time-dependent harmonic potential opposed transverse displacement, in accord with recent simulation findings. A tube radius of 0.8 microm was determined, close to the predicted value (0.5 microm). Three relaxation modes (approximately 0.4, 5, and 34 s) were measured following transverse displacement, consistent with predicted relaxation mechanisms.     

Effective refractive index and intermolecular forces associated with a phase of functional groups

Cases in which a functional groups form distinct phases are known in material science in general and specifically in polymer and surfactant sciences. To calculate the van der Waals forces associated with such phases there is a need to evaluate the refractive index of those phases. We expand and generalize a method to estimate the refractive index of such ‘functional group phase’ and discuss how to use the refractive indices to calculate the interaction energies associated with such functional group phases and thereby modify the total theoretically calculated van der Waals forces.     

Effect of dipole-dipole intermolecular forces in the vibration spectra of organic compounds

The potential energy of a polar liquid is derived from the electrostatic interaction of point dipoles, taking into account the formation of local groups with short-range order with minimum energy. The methods of classical mechanics are used to estimate the effects of interaction on the normal vibration frequencies. It is shown that interaction increases the frequencies of low-frequency dipole-rotation vibrations; frequencies of other types may increase or decrease.I am indebted to Professor N. A. Prilezhaeva for discussing these results.     

Effect of dipole-dipole intermolecular forces on the vibrational spectra of organic compounds

Raman line widths were measured for monosubstituted benzene, -picolene and -chloronaphthalene in the liquid phase at various temperatures. Factors affecting the linewidth are analyzed theoretically.The authors are greatly indebted to N. A. Prilezhaeva for her constant attention and valuable advice.     

Development of dipole-dipole intermolecular forces in the vibration spectra of organic compounds

Possible line broadening of the vibrational spectra of organic liquids as a result of intermolecular vibrational reactions has been theoretically assessed. It has been shown that the frequency scattering connected with fluctuations in the energy of local electrostatic forces can explain the width observed in some cases. It has been found possible to link line broadening with the temperature behavior of the frequencies.The author would like to express his sincere thanks to N. A. Prilezhaev for his interest in this work and for valuable discussions of it.     

Manifestation of dipo le-di pole intermolecular forces in organic compounds

Raman spectra were obtained for -, -, and -picolines in the gaseous state and in the liquid at various temperatures. Most of the observed frequencies were assigned by comparison with the spectra of pyridine and toluene. A phase shift was observed in the frequencies on passing from gas to liquid; it was interpreted in terms of local dipole-dipole interactions, and a correlation was established with the dipole moment of the molecule. The widths of a series of lines in the spectra of the picolines in the liquid state were measured. Analysis of the results revealed a relative contribution from Brownian rotational movement of the molecules and fluctuations of the dipole-dipole forces.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 8, pp. 87–93, August, 1968.The authors thank M. F. Vuks for kindly providing the compounds.     

Manifestation of dipole-dipole intermolecular forces in VI-brational spectra of organic compounds

The temperature dependence of line width in the Raman spectra of acetonitrile and benzonitrile in the liquid state was investigated experimentally by photographic and photoelectric methods. By excluding the effect of dipole-dipole broadening from the observed line width, the temperature dependence of the component width due to rotational Brownian motion of the molecules in the liquid was revealed. It was found that the parameters of the rotational Brownian motion undergo sharp changes near the crystallization points of the liquids. To explain this effect it is suggested that molecular association occurs in the liquid at low temperatures under the influence of dipole-dipole forces. By simple calculations, an assignment is made of the frequencies of benzonitrile in the low-frequency region, and the forms of the molecular vibrations are established.