Physical orientation-dependent

The basic effects on organic molecules of binding to solid surfaces are a function of many possible steric and electronic interactions. However, the ultimate photochemical fate of bound molecules will depend primarily upon their specific physical orientations while adsorbed on the solid surface. Photoreactivity will depend upon which part or parts of the molecules are actually... 

The 55Mn2+ ion, S = 5/2,1 = 5/2, was studied in a-ZnV207. The orientation dependence of the spectra at 250 GHz was measured32 using a goniometer in a quasi-optical spectrometer at 253 K. Two magnetically inequivalent, but physically equivalent, sites were detected that could be described by the same set of spin Hamiltonian parameters. The (/-factor was found to be isotropic with a value close to 2 and the ZFS was 6 GHz. 

The molecules in a monomolecular film, especially at high surface concentrations, are often arranged in a simple manner, and much can be learned about the size, shape and orientation of the individual molecules by studying various properties of the monolayer. Monomolecular films can exist in different, two-dimensional physical states, depending mainly on the magnitude of the lateral adhesive forces between the film molecules, in much the same way as three-dimensional matter. 

To make a product suitable for sale, the various contaminants and undesirable constituents contained in the raw gas must be removed. The first step is to separate the gas from any liquids and/or solids. This initial separation usually is carried out in near proximity to the producing well. The separators used depend primarily upon the difference in density between the gas and the liquid for separating the two phases. These separators may be classified as vertical, horizontal, or spherical, depending on their geometry and physical orientation.8... 

Dick, L.A., Haes, A.J., and Van Duyne, R.P. (2000) Distance and orientation dependence of heterogeneous electron transfer a surface-enhanced resonance Raman scattering study of cytochrome c bond to carboxylic acid terminated alkanethiols adsorbed on silver electrodes. Journal of Physical Chemistry B, 104, 11752-11762. 

T is the fluorescence lifetime and Rq the critical transfer radius for donor-donor transport (29). For experiments in high viscosity media, the chromophores are essentially static and the appropriate orientation dependent Rq must be used (8.21). N is the number of chromophores in the system. P(r 2) lb] 2 probability that there is a chromophore at a distance r 2 from chromophore 1. The Integral is over the physical space and A is the appropriate normalization factor. Next, it is necessary to average over the possible positions of the initially excited chromophore... 

By far the most important application of liquid crystals is display devices. Liquid crystal displays (LCDs) are used in watches, calculators, and laptop computer screens, and for instrumentation in cars, ships, and airplanes. Several types of LCDs exist. In general their value is due to the fact that the orientation of the molecules in a nematic phase substance can be altered by the application of an external electric field, and that liquid crystals are anisotropic fluids, that is, fluids whose physical properties depend on the direction of measurement. It is not pure liquid crystalline compounds that are used in LCDs, but liquid crystal mixtures having optimized properties. 

Physical origin of dielectric loss The foregoing conclusions correspond to a static description or cases for which the polarization can perfectly follow the oscillation of the electric field. Indeed, the electric field orientation depends on time with a frequency equal to 2.45 GHz (the electric field vector switches its orientation approximately every 10 s). The torque exercised by the electric field induces rotation of polar molecules, but they cannot always orient at this rate. The motion of the particles will not be sufficiently rapid to build up a time-dependent polarization P(t) that is in equilibrium with the electric field at any moment. This delay between electromagnetic stimulation and molecular response is the physical origin of the dielectric loss. 

The interaction between small molecules and oxide surfaces is characterized by a delicate balance of attractive and repulsive contributions which have different physical and chemical origin. In most cases, several of these contributions have the same order of magnitude, but different distance and orientation dependence. Reliable results for adsorption geometries and energies can be only obtained if all of these contributions are properly taken into account and are quantitatively correctly described. Otherwise, one will get results of doubtful quality, maybe accidentally even the correct answer. 

Du, X.H., Belegundu, U., and Uchino, K. (1997) Crystal orientation dependence of piezoelectric properties in lead zirconate titanate theoretical expectations for thin films. Jpn. J. Appl. Phys., 36 (9A), 5580-5587. Reprinted with permission from American Institute of Physics. 

The physical meaning of this parameter is the description of orientation-dependent intermolecular interactions. The parameter is used in many correlations for the estimation of thermophysical properties, especially in cubic equations of state. The definition makes sense, as vapor pressures as a function of temperature are... 

The description of molecule-molecule potentials is greatly complicated by the orientation dependence. One approach is to expand the potential using the type of function described in Section 1, but this is unsatisfactory for all except nearly spherical molecules like H2 and perhaps a few others, because the expansion diverges at physically accessible distances. Another is to treat a molecule as a semi-rigid collection of spherical atoms, and this usually gives a better account of the dispersion and the repulsive part of the potential. To this may be added the multipole expansion of the electrostatic energy. 

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