Pure reorientation

The purely reorientational broadening mechanism with a single threefold quasidegenerate subbarrier level is characteristic of the valence vibration spectral line for OH groups on Si02 surface. Equation (4.2.22) describes the observed temperature... 

Prompers and Briischweiler showed by quasiharmonic analysis that the conformational partition function of a globular protein sampled on the ns time scale can be factorized in good approximation into purely reorientational part, which determines heteronuclear NMR spin relaxation, and a remaining part that includes other types of intramolecular motions. Thus a thermodynamic interpretation of NMR relaxation parameters in proteins in the presence of motional correlations can be given. 

Pure Reorientation of the Azo-Dye Chromophore Molecuies or Azo-Dye Molecular Solvates... 

Besides a chemical reaction, the UV light can induce an asymmetric potential field under which the stable configuration is characterized by the dye absorption oscillator perpendicular to the induced light polarization. One of the possible photoaligning mechanisms in azo-dye films is a pure reorientation of azo-dye molecules [10, 18, 42, 43]. Diffusion mechanisms of the azo-dye reorientation can be used to explain this phenomenon. 

As follows from Table 3.1, pure reorientation (diffusion) is the most suitable mechanism for LC photoalignment. The commercialization of the materials produced by the Die Corporation (Japan) is expected soon [45, 46]. The first target should be the photoaligning of monomers and LC polymers for phase retarder applications (Chapter 5). Photoaligning with azo-dye layers will be considered below. 

Pure reorientation Small [12] High, com- High, com- High [37] Easy - the only... 

The monolayer resulting when amphiphilic molecules are introduced to the water—air interface was traditionally called a two-dimensional gas owing to what were the expected large distances between the molecules. However, it has become quite clear that amphiphiles self-organize at the air—water interface even at relatively low surface pressures (7—10). For example, x-ray diffraction data from a monolayer of heneicosanoic acid spread on a 0.5-mM CaCl2 solution at zero pressure (11) showed that once the barrier starts moving and compresses the molecules, the surface pressure, 7T, increases and the area per molecule, M, decreases. The surface pressure, ie, the force per unit length of the barrier (in N/m) is the difference between CJq, the surface tension of pure water, and O, that of the water covered with a monolayer. Where the total number of molecules and the total area that the monolayer occupies is known, the area per molecules can be calculated and a 7T-M isotherm constmcted. This isotherm (Fig. 2), which describes surface pressure as a function of the area per molecule (3,4), is rich in information on stabiUty of the monolayer at the water—air interface, the reorientation of molecules in the two-dimensional system, phase transitions, and conformational transformations. 

The vibrational dynamics of water solnbilized in lecithin-reversed micelles appears to be practically indistingnishable from those in bulk water i.e., in the micellar core an extensive hydrogen bonded domain is realized, similar, at least from the vibrational point of view, to that occurring in pure water [58], On the other hand, the reorientational dynamics of the water domain are strongly affected, due to water nanoconfmement and interfacial effects [105,106],... 

It is important from a practical viewpoint to predict the shear viscosity of mixtures from those of pure melts. For alkali nitrate melts, a linear dependence has been found between the reorientational line width obtained by Raman measurements and the ratio of temperature divided by shear viscosity.For NO3 ions, the depolarized Raman scattering from 1050cm" total stretching vibrational mode (Al) has a contribution to the line width L, which is caused by the reorientational relaxation time of the Csv axis of this ion. The Stokes-Einstein-Debye(SED) relation establishes a relation between the shear viscosity r of a melt and the relaxation time for the reorientation of a particle immersed in it ... 

One may wonder whether a purely harmonic model is always realistic in biological systems, since strongly unharmonic motions are expected at room temperature in proteins [30,31,32] and in the solvent. Marcus has demonstrated that it is possible to go beyond the harmonic approximation for the nuclear motions if the temperature is high enough so that they can be treated classically. More specifically, he has examined the situation in which the motions coupled to the electron transfer process include quantum modes, as well as classical modes which describe the reorientations of the medium dipoles. Marcus has shown that the rate expression is then identical to that obtained when these reorientations are represented by harmonic oscillators in the high temperature limit, provided that AU° is replaced by the free energy variation AG [33]. In practice, tractable expressions can be derived only in special cases, and we will summarize below the formulae that are more commonly used in the applications. 

There are also several papers describing adsorption of quinoline. Sawamoto [143] have studied adsorption and reorientation of quinoline molecules at Hg electrodes by recording differential capacity-potential and differential capacity-time plots using the flow-injection method. Adsorption of quinoline was found reversible at any potential, with the possibility of reorientation of the molecules at the interface. Ozeld etal. [144] have studied adsorption, condensation, orientation, and reduction of quinoline molecules at pure Hg electrode from neutral and alkaline solutions, applying electrochemistry and Raman microprobe spectroscopy. The adsorbed quinoline molecules changed their orientation from the flat at —0.1 V > E > —0.3 V, to the upright at < —0.5 V. At potentials —0.3 V > > —0.5 V, both orientations were observed. Later, Ozeld et al. [145] have extended the studies on reorientation of quinolinium ions at the Hglacidic aqueous solution interface. For these conditions, the specific adsorption of quinoline was not observed. 

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