Repulsion electric dipoles

Forces Molecules are attracted to surfaces as the result of two types of forces dispersion-repulsion forces (also called London or van der Waals forces) such as described by the Lennard-Jones potential for molecule-molecule interactions and electrostatic forces, which exist as the result of a molecule or surface group having a permanent electric dipole or quadrupole moment or net electric charge. 

Van der Waals forces are the electrostatic a ttractions between the electrons in one molecule and the nuclei of an adjacent molecule minus the molecules inter electronic and intemuclear repulsive forces. In about 1930, Fritz London showed that these forces are caused by the attraction between an electric dipole in some molecule and the electric dipole induced in an adjacent one. Therefore, van der Waals forces result from random fluctuations of charge and are important only for molecules that are very close together—in particular, for neighboring molecules. 

In the above discussion, we have only considered the effects due to the CTE-CTE repulsion, which contribute to the resonant nonlinear absorption (as well as to other resonant nonlinearities) by the CTE themselves. Here, however, we want to mention a more general mechanism by which the nonlinear optical properties of media containing CTEs in the excited state can be enhanced. This influence is due to the strong static electric field arising in the vicinity of an excited CTE, If, for example, the CTE (or CT complex) static electric dipole moment is 20 Debye, at a distance of 0.5 nm it creates a field Ecte of order 107 V/cm. Such strong electric fields have to be taken into account in the calculation of the nonlinear susceptibilities, because they change the hyperpolarizabilities a, / , 7, etc. of all molecules close to the CTE. For instance, in the presence of these CTE induced static fields, the microscopic molecular hyperpolarizabilities are modified as follows... 

The AFM creates atomic level resolution images of the surfaces of noncon-ductive specimens, using the quantum mechanical phenomenon of repulsive atomic force. The AFM records the repulsive forces that occur when electron clouds of two atoms, one in the microscope probe and the other at the sample surface, are in close proximity to each other. In most AFMs, the sample is mounted on the piezoelectric tube, so the sample moves in relation to a stationary tip. As the sample is very close to the probe, the fluctuations in electric dipole moment of the interacting atoms create a repulsive action between atoms of the specimen and atoms of the probe. As the probe is deflected by the atoms on the surface of the specimen, its movement is intercepted by a laser beam, which transmits the information to the computer for image generation. 

In order to compute or interpret photodissociation a(E) functions, it is necessary to know (i) the potential energy curve of the initial state (ii) the potential energy curves of all energetically accessible excited electronic states (both purely repulsive states and the above dissociation repulsive region of bound states) (iii) the electric dipole transition moment function between the initial and final state (iv) the (R- dependent) interactions among the set of electronic... 

Energy/ , is the total electronic energy including nuclear repulsion in hartrees at the calculated equilibrium geometry IX, 0, and Roh are the calculated electric dipole moment, equilibrium bond angle, and equilibrium bond length. 

In 1968, Hutchins et al. [41] reported that there is a widespread phenomenon in structural chemistry that the conformations are strongly disfavored if the unshared electron pairs on nonadjacent atoms are parallel or syn-axial, as is the case, for example, in 40 in Fig. 2.15. This effect is thought to be due to the repulsion of electric dipoles engendered by the unshared electron pairs. For obvious reasons, Eliel named this phenomenon the rabbit-ear effect. ... 

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