Short range structure

Ultimately physical theories should be expressed in quantitative terms for testing and use, but because of the eomplexity of liquid systems this can only be accomplished by making severe approximations. For example, it is often neeessary to treat the solvent as a continuous homogeneous medium eharaeterized by bulk properties such as dielectric constant and density, whereas we know that the solvent is a molecular assemblage with short-range structure. This is the basis of the current inability of physical theories to account satisfactorily for the full scope of solvent effects on rates, although they certainly can provide valuable insights and they undoubtedly capture some of the essential features and even cause-effect relationships in solution kinetics. Section 8.3 discusses physical theories in more detail. 

The division of the interface into an inner layer and a diffuse layer has been a matter of discussion in view of the molecular dimensions of the inner layer.122-126,279-285 However, the contribution of a constant capacitance is an experimental fact. Furthermore, molecular theories for electrolytes near a charged hard wall282 as well as phenomenological nonlocal electrostatic theories283 predict such a component without artificial introduction of any inner layers. This turns out to be an effect of the short-range structure of the solvent.279-285... 

The surface reconstruction of Au(110) is more rapid than that of Au(l 1 l)andAu(100).257,467,504-514,516-518Au(533)andAu(311), localized in the [(110)-(100)] zone, and Au(221) and (331), localized in the [(111)-(110)] zone, exhibit stable terrace step structural arrangements largely free from disordering and facetting 485 Au(210) and (410), localized in the [(100)-(110)] zone, display only a short-range structural order related to the especially open nature of these faces. 

In contrast to the reconciliation of short-range structure with net random coil-like behavior, the presence of long-range order in even the most highly denatured states is perhaps more problematic (Shortle and... 

Figure 1.17 The sorption rates of mercaptopropyl-functionalized ORMOSIL depend on the relative long-range versus short-range structural order/disorder and their intrinsic hydrophobicity. Ordered materials with 20-30% alkylation perform best. (Reproduced from ref. 38, with permission.)...

Figure 1.9 Possible alignments of two dipolar molecules that can lead to attraction and short-range structuring of liquids...

By their nature, and in contrast with microscopic and scattering techniques that are used to elucidate long-ranged structure, spectroscopic methods interrogate short-range structure such as interactions between fixed ions in side chains and counterions, main chain conformations and conformational dynamics, and the fundamental hopping events of water molecules. The most common methods involve infrared (mid-IR and to a much lesser extent near- and far-IR) and solid-state NMR spectroscopies, although other approaches, such as molecular probes, have been utilized. 

S. Sen, H. Maekawa and G. N. Papatheodorou, Short-range structure of invert glasses along the pseudo-binary join MgSi03-Mg2Si04 results from Si and Mg MAS NMR spectroscopy. /. Phys. Chem. B, 2009,113,15243-15248. 

Van Soest, J. J. G., Tournois, H., de Wit, D., Vliegenthart, J. F. G. (1995). Short-range structure in (partially) crystalline potato starch determined with attenuated total reflectance Fourier-transform IR spectroscopy. Carbohydrate Research, 279, 201-214. 

Di Cicco, A., and Minicucci, M., Solid and liquid short-range structure determined by EXAFS multiple-scattering data analysis, /. Synchrotron Rad., 6, 255-257,1999. 

Di Cicco, A., Taglienti, M., Minicucci, M., and Filipponi, A., Short-range structure of solid and liquid AgBr determined by multiple-edge X-ray absorption spectroscopy, Phys. Rev. B, 62, 12001-12013, 2000. 

Vitreous silica is considered the model glass-forming material and as a result has been the subject of a large number of x-ray, neutron, and electron diffraction studies (12—16). These investigations provide a detailed picture of the short-range structure in vitreous silica, but questions about the longer-range structure remain. 

Extended x-ray absorption fine structure measurements (EXAFS) have been performed to investigate the short-range structure of TbFe films (46). It is observed that there is an excess number of Fe—Fe and Tb—Tb pairs in the plane of the amorphous film and an excess number of Tb—Fe pairs perpendicular to film. The increase of K with the substrate temperature for samples prepared by evaporation is explained by a rearrangement of local absorbed atom configurations during the growth of the film (surface-induced texturing) (47). 

Gamba Z, Klein ML. Short-range structure of liquid pyrrole. J Chem Phys 1990 92 6973-6974. 

Amorphous ice has been studied in some detail by both X-ray and neutron diffraction [738-740]. The O- -O pair-correlation functions are similar to those of liquid water, except that on condensing on very cold surfaces, i.e., 10 K, there is an extra sharp peak at 3.3 A. This indicates some interpenetration of the tetrahedral disordered ice-like short-range structures. It appears that none of the many proposed atom-atom potential energy functions can simulate a structure for liquid water that predicts pair-correlation functions which are a satisfactory fit to the experimental data [741, 742]. Opinions seem to differ as to whether the discrepancy is in the theory or the experiments. 

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