Anisotropic molecular bond

The connection between anisotropic molecular motion and nuclear relaxation was derived by Woessner as early as 1962 [161]. Accordingly, the dipole-dipole relaxation time of a carbon nucleus is a function of the diagonal components R, R2, and R3 of the rotational diffusion tensor and the cosines X, p, and v of the angles assumed by the C —H bonds relative to the principal axes of this tensor ... 

An intricate diffusion limited scenario was observed in the low-temperature aggregation of PVBA and the related species PEBA (4-[(pyrid-4-yl-ethynyl)]-benzoic acid) on Ag(lll) [78,79]. The operation of anisotropic hydrogen bonding between the molecular endgroups in conjunction with the smoothness of the substrate leads to the formation of molecular networks, as demonstrated by the STM data in Fig. 6. At higher... 

As a final example in this subsection we mention the recent study of Zillich and Whaley who examined LiH solvated in He clusters with up to 100 atoms. The authors used a path integral Monte Carlo simulation approach, whose details shall not be discussed further here. The LiH-He interaction potential was found to be highly anisotropic with attractions for He approaching the molecule in a direction parallel to the molecular axis, but with strong repulsions for He approaching the molecule in a direction perpendicular to the molecular bond. Despite these repulsions, the authors found that LiH prefers to occupy central regions of the LiH He clusters for n larger than 10-15. 

A new through-bond correlation method for disordered solids has been proposed. The new approach is based on the uniform-sign cross-peak double quantum filtered correlation spectroscopy experiment, which is a refocused version of the popular double quantum filtered correlation spectroscopy experiment in liquids. Its key feature is that it provides in-phase and doubly absorptive line shapes, which renders it robust for chemical shift correlation in solids. It has been shown that both theory and experiment point to distinct advantages of this protocol, which are illustrated by several experiments under challenging conditions, including fast MAS up to 30kHz, anisotropic molecular motion, and correlation spectroscopy at the natural abundance isotope level. 

The loss of coordinatively bonded aqua ligands at such a low temperature suggests some kinds of structural transformation in the solid state. This photoreactivity confirms the formation of a thermodynamically stable ladder structure by the cooperative anisotropic molecular movements of the adjacent ID chains occur during the desolvation process (Figure 12), which is stabilized by Ag- -Ag and % % interactions. A similar structural transformation of a linear CP [Cd(bpe)(CH3C00)2(H20)] (19) to a ladder structure by thermal dehydration was also successfully monitored because of its photoreactivity. ... 

As mentioned frequently the mechanical and optical response of molecules — and of their crystallites — is highly anisotropic. Depending on the property under consideration the carriers of the molecular anisotropy are the bond vectors (infrared dichroism), chain segments (optical and mechanical anisotropy), or the end-to-end vectors of chains (rubber elastic properties). For the representation of the ensuing macroscopic anisotropies one has to recognize, therefore, the molecular anisotropy and the orientation distribution of the anisotropic molecular units (Fig. 1.9.). Since these are essentially one-dimensional elements their distribution and orientation behavior can be treated as that of rods such a model had been used successfully to explain the optical anisotropy [78], and the anisotropies of thermal conductivity [79], thermal expansion or linear compressibility [80], and Young s modulus [59,... 

The molecular bond energy that derives from intermolecular interactions inside the LFSs gives an anisotropic contribution 5V(r,Q) to the overall potential of the system V(r,D), which is thus given by ... 

The parameter /r tunes the stiffness of the potential. It is chosen such that the repulsive part of the Leimard-Jones potential makes a crossing of bonds highly improbable (e.g., k= 30). This off-lattice model has a rather realistic equation of state and reproduces many experimental features of polymer solutions. Due to the attractive interactions the model exhibits a liquid-vapour coexistence, and an isolated chain undergoes a transition from a self-avoiding walk at high temperatures to a collapsed globule at low temperatures. Since all interactions are continuous, the model is tractable by Monte Carlo simulations as well as by molecular dynamics. Generalizations of the Leimard-Jones potential to anisotropic pair interactions are available e.g., the Gay-Beme potential [29]. This latter potential has been employed to study non-spherical particles that possibly fomi liquid crystalline phases. 

The range of systems that have been studied by force field methods is extremely varied. Some force fields liave been developed to study just one atomic or molecular sp>ecies under a wider range of conditions. For example, the chlorine model of Rodger, Stone and TUdesley [Rodger et al 1988] can be used to study the solid, liquid and gaseous phases. This is an anisotropic site model, in which the interaction between a pair of sites on two molecules dep>ends not only upon the separation between the sites (as in an isotropic model such as the Lennard-Jones model) but also upon the orientation of the site-site vector with resp>ect to the bond vectors of the two molecules. The model includes an electrostatic component which contciins dipwle-dipole, dipole-quadrupole and quadrupole-quadrupole terms, and the van der Waals contribution is modelled using a Buckingham-like function. 

As in the case of iron chemistry, most valuable information concerning bond properties (anisotropic electron population of molecular orbitals) and local structure may be extracted from quadrupole-split Ru spectra. This has been... 

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