Anisotropy of interactions

In the extreme case of grazing incidence, a field component exists only normal to the surface. Therefore an interaction is possible exclusively with transition moments or components thereof, orientated perpendicular to the surface. This anisotropy of interaction can also be explained by selection rules, which are based on symmetry consideration and include the mirror image of the analyte produced by the metallic surface. 

In the absenee of anisotropy introdueed by speeifie surfactant-surfactant interactions, a spherical droplet model is reasonable beeause it tends to minimize the surfaee energy. Deviations from spherical symmetry occru" because of the finite size and anisotropy of surfaetant moleeules and the anisotropy of interactions. Many early experimental data were interpreted on the assumption of spherieal structures. In seminal Monte Carlo studies by Haan and Pratt... 

Orientational relaxation plays a key role in many relaxation processes, such as polarization and DR, SD and quadmpolar relaxation. It profoundly influences the dynamics of the many important chemical reactions, such as the electron and proton transfer reactions in a polar liquid The orientational relaxation of an anisotropic molecule in liquid clearly depends on the density and the temperature of the liquid and also on the nature of the anisotropy of interaction potential. It may also be coupled to the translational modes of the liquid and the internal modes of the molecule. Orientational relaxation in a liquid can show rich and diverse dynamic behavior. 

CoUisional transfer of rotational to translational energy is very fast so that it can be separated from translational relaxation under certain restrictive conditions only. Estimation of the mean square energy transfer shows that the condition ((AE) ) (kT) is fulfilled either when the anisotropy of interaction... 

The dipole density profile p (z) indicates ordered dipoles in the adsorbate layer. The orientation is largely due to the anisotropy of the water-metal interaction potential, which favors configurations in which the oxygen atom is closer to the surface. Most quantum chemical calculations of water near metal surfaces to date predict a significant preference of oxygen-down configurations over hydrogen-down ones at zero electric field (e.g., [48,124,141-145]). The dipole orientation in the second layer is only weakly anisotropic (see also Fig. 7). 

The orientational structure of water near a metal surface has obvious consequences for the electrostatic potential across an interface, since any orientational anisotropy creates an electric field that interacts with the metal electrons. Hydrogen bonds are formed mainly within the adsorbate layer but also between the adsorbate and the second layer. Fig. 3 already shows quite clearly that the requirements of hydrogen bond maximization and minimization of interfacial dipoles lead to preferentially planar orientations. On the metal surface, this behavior is modified because of the anisotropy of the water/metal interactions which favors adsorption with the oxygen end towards the metal phase. 

From the NMR data of the polymers and low-molecular models, it was inferred that the central C—H carbons in the aliphatic chain in polymer A undergo motions which do not involve the OCH2 carbons to a great extent. At ambiet temperatures, the chemical shift anisotropy of the 0(CH2)4 carbons of polymer A are partially averaged by molecular motion and move between lattice positions at a rate which is fast compared to the methylene chemical shift interaction. 

As has been noticed by Gelbart and Gelbart [7], the predominant orientational interaction in nematics results from the isotropic dispersion attraction modulated by the anisotropic molecular hard-core. The anisotropy of this effective potential comes from that of the asymmetric molecular shape. The coupling between the isotropic attraction and the anisotropic hard-core repulsion is represented by the effective potential... 

The temperature dependence of the magnetic hyperfine splitting in spectra of interacting nanoparticles may be described by a mean field model [75-77]. In this model it is assumed that the magnetic energy of a particle, p, with volume V and magnetic anisotropy constant K, and which interacts with its neighbor particles, q, can be written... 

Figure 5. Fluorescence anisotropy of F-D labelled heparin-antithrombin interaction. F-D-heparin (0.02 fluoresceins per uronic acid) at 0.1 mg/ml was incubated with different concentrations of antithrombin (open circles) or bovine serum albumin (solid diamonds) in 20 mM sodium phosphate buffer, pH 7.4.

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