Intermolecular forces

1975 ◽  
Vol 272 (915) ◽  
pp. 5-12 ◽  
Keyword(s):  
Long Range ◽  
Molecular Interactions ◽  
Short Range ◽  
Intermolecular Forces ◽  
Electron Exchange ◽  
Inverse Power ◽  
Charge Distributions ◽  
Electrostatic Component ◽  
Electrostatic Induction ◽  
Long Range Interactions

The nature of molecular interactions is examined. Intermolecular forces are divided into long-range and short-range components; the former operate at distances where the effects of electron exchange are negligible and decrease as an inverse power of the separation. The long-range interactions may be subdivided into electrostatic, induction and dispersion contributions, where the electrostatic component is the interaction of the permanent charge distributions and the others originate in the fluctuations in the distributions. Typical magnitudes of the various contributions are given. The forces between macroscopic bodies are briefly considered, as are the effects of a medium. Some of the manifestations of molecular interactions are discussed.

INTERMOLECULAR POTENTIALS IN LIQUID CRYSTALS: COMPARISON BETWEEN SIMULATIONS AND NMR EXPERIMENTS

1999 ◽  
Vol 10 (02n03) ◽  
pp. 403-413 ◽  
Author(s):  
RAYMOND T. SYVITSKI ◽  
JAMES M. POLSON ◽  
E. ELLIOTT BURNELL
Keyword(s):  
Liquid Crystals ◽  
Long Range ◽  
Short Range ◽  
Intermolecular Forces ◽  
Order Parameters ◽  
Intermolecular Potential ◽  
Nmr Data ◽  
Long Range Interactions ◽  
Orientational Ordering ◽  
Best Fit

The anisotropic intermolecular forces responsible for the orientational ordering in liquid crystals are probed by comparing Monte Carlo (MC) simulations with experimental nuclear magnetic resonance (NMR) results for solutes in nematic liquid crystals. In a special liquid crystal mixture where all long-range interactions are assumed to be minimized, the models for short-range interactions which best fit NMR experimental solute order parameters also best fit solute order parameters from MC simulations of hard ellipsoids. This is taken as an indication that in this special mixture the intermolecular potential is dominated by short-range forces. However, for liquid crystals where long-range interactions are important, simulations of hard ellipsoids with point quadrupoles cannot reproduce even the gross effects observed with experimental NMR data.

Development of lateral interactions in the infant visual system

1992 ◽  
Vol 8 (1) ◽  
pp. 3-8 ◽  
Author(s):  
Samuel Sokol ◽  
Vance Zemon ◽  
Anne Moskowitz
Keyword(s):  
Visual System ◽  
Long Range ◽  
Short Range ◽  
Second Harmonic ◽  
Harmonic Component ◽  
Frequency Component ◽  
Human Infants ◽  
Long Range Interactions ◽  
Harmonic Components ◽  
Inhibitory Interactions

AbstractThe development of lateral inhibitory interactions in the infant visual system, as reflected by the visual-evoked potential (VEP), was studied using a radial, asymmetrical windmill-dartboard stimulus. This contrast-reversing stimulus generates VEP responses with a strong fundamental frequency component and an attenuated second harmonic component (relative to that obtained using a symmetrical stimulus). These two harmonic components reflect distinct phenomena, and appear to be the result of short-range (the fundamental) and long-range (attenuated second harmonic) lateral inhibitory interactions elicited by differential luminance-modulation of contiguous spatial regions. We studied the development of the short-and long-range interactions at 100% and 30% contrast in human infants using both VEP amplitude and phase measures. Attenuation of the second harmonic (long-range interactions) was adult-like by 8 weeks of age while the strength of the fundamental (short-range interactions) was adult-like by 20 weeks suggesting a differential development of long-range and short-range interactions. In contrast, corresponding phase data indicated significant immaturities at 20 weeks of age for both the short-and long-range components.

ON A COMBINED SHORT-RANGE AND LONG-RANGE INTERACTING EARTHQUAKE MODEL

2000 ◽  
Vol 11 (05) ◽  
pp. 913-919
Author(s):  
A. S. ELGAZZAR ◽  
E. AHMED
Keyword(s):  
Long Range ◽  
Short Range ◽  
Self Organized ◽  
Long Range Interactions ◽  
Earthquake Model

A self-organized critical earthquake model is proposed taking into account the effect of both short-range and long-range interactions. The model obeys both Gutenberg–Richter and Omori laws in addition to being more realistic than other models.

On the chemical consequences of long-range interactions in chiral systems

1975 ◽  
Vol 28 (6) ◽  
pp. 1161 ◽  
Author(s):  
PE Schipper
Keyword(s):  
Long Range ◽  
Electrostatic Interactions ◽  
Intermolecular Forces ◽  
Statistical Thermodynamic ◽  
Thermodynamic Quantities ◽  
Redox Potentials ◽  
Chiral Molecules ◽  
Long Range Interactions ◽  
Three Stages ◽  
Chiral Systems

The chemical manifestations of discrimination in long-range (non- contact) interactions of chiral molecules are analysed in three stages. A simple thermodynamic model is used to establish a method of presenting experimental data (such as differences in racemization rates, solubilities and redox potentials of pure enantiomers in non- associating chiral media) in terms of well defined thermodynamic discriminations. The thermodynamic quantities are then related directly to discriminations in intermolecular interactions through a statistical thermodynamic treatment. Estimates of the discrimination in intermolecular forces from experimental thermodynamic data suggest that only electrostatic interactions are sufficiently large to account for the experimentally observed values of the discrimination.

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