Polarizability orientation

Linear absorption and fluorescence spectra for the series of symmetrical cationic polymethines with 5-butyl-7,8-dihydrobenzo[ /]furo 2,3 /lindolium terminal groups are shown in Fig. 14 for solvents of different polarity. It is known that the polarity of solvents can be characterized by their orientational polarizability, which is given by Af = (e- l)/(2e + 1) — (n2 - l )/(2n2 +1), where e is the static dielectric constant and n is the refractive index of the solvent [41], Calculated A/values... 

Zdzislaw, S. Gordon, T., Optical anisotropy in lipid bilayer membranes Coupled plasmon waveguide resonance measurements of molecular orientation, polarizability, and shape, Biophys. J. 2001, 80, 1557 1567... 

When Stokes shifts are plotted as a function of the orientation polarizability A f (Lippert s plot, see Section 7.2.2), solvents are distributed in a rather complex manner. A linear relationship is found only in the case of aprotic solvents of relatively low polarity. The very large Stokes shifts observed in protic solvents (methanol, ethanol, water) are related to their ability to form hydrogen bonds. 

There are three common modes of polarizability in organic molecules, which are, in order of increasing resonant frequency, orientation polarizability, atomic polarizability, and electronic polarizability. ... 

Kaatze, U. Orientation Polarizability and Molecular Motion of Water in Water and Aqueous Solutions, in i4). 

The polarizability of a polar molecule has two components an electronic polarizability, ye, due to the displacement of electrons, and an orientational polarizability, y, due to the rotation of the permanent dipole in an electric field. In the vapor phase, assuming that the molecule can rotate freely, the orientational polarizability is given by the Langevin function. Therefore, for low effective electric fields (pEe- kT)... 

The partial (because of the disorientating effect of thermal motion) alignment of permanent dipoles (orientation polarizability, a ). This contribution accounts for the temperature-dependence of the dielectric constant, since increased thermal agitation tends to scramble the permanent dipoles. Their orientation polarizability, aM, is defined according to the strength of the (permanent) dipole moment, n, of the molecule... 

Thus, it is summarized that the main contributors to the van der Waals attraction are the deformation polarizability independent of the presence of the permanent dipole and the orientation polarizability that is the average effect of the rotation of the molecule, depending on temperature in the electric field. 

Polarizability (of a molecule) — There are numerous different mechanisms that contribute to the total polarizability of a molecule. The three most important of these are termed electron polarizability, molecular-distortion polarizability, and orientation polarizability. All these parameters are measured as statistical averages over large numbers of molecules present in the bulk phase. (1) -> Electron polarizability a is a measure of the ease with which electrons tend to be displaced from their zero-field positions by the applied -> electric field. Thus, the electron polarizability of a molecule is defined as the ratio of induced dipole moment pincj (coulomb meters) to the inducing electric field E (volts per meter) ... 

Molecular distortion polarizability is a measure of the ease with which atomic nuclei within molecules tend to be displaced from their zero-field positions by the applied electric field. (3) Orientation polarizability is a measure of the ease with which dipolar molecules tend to align against the applied electric field. The electron polarizability of an individual molecule is related to the -> permittivity (relative) of a dielectric medium by the -> Clausius-Mossotti relation. 

This equation clearly shows the effect of the secondary solvation. It turns out that the orientation polarizabilities % and depend on the square of the permanent dipole moments of the molecules. Water has a higher dipole moment than most nonelectrolytes. When S is less than Sq and there is salting out. HCN is an... 

The dielectric constant is a natural choice of order parameter to study freezing of dipolar liquids, because of the large change in the orientational polarizability between the liquid and solid phases. The dielectric relaxation time was calculated by fitting the dispersion spectrum of the complex permittivity near resonance to the Debye model of orientational relaxation. In the Debye dispersion relation (equation (3)), ij is the frequency of the applied potential and t is the orientational (rotational) relaxation time of a dipolar molecule. The subscript s refers to static permittivity (low frequency limit, when the dipoles have sufficient time to be in phase with the applied field). The subscript oo refers to the optical permittivity (high frequency limit) and is a measure of the induced component of the permittivity. 

By combining Equations (41) and (44), the orientation polarizability of a dipolar molecule can be calculated as... 

However there are exceptions in a very high electrical held, such as when water molecules are placed near a small ion or when the temperature is very low where kT is very small, the orientation polarizability concept breaks down, and a dipolar molecule completely aligns along the held however the induced polarizability still applies. 

According to the accepted photo-physical concepts on the influence of the medium on emission spectra, the effects observed may be divided into general (non-specific) and specific ones.7 General effects result in changes in orientation polarizability of the emitter microenvironment whose value depends on dielectric constant and refractive index of the medium. Maximum spectral shift is observed for the emitters with maximum changes in dipole moments upon excitation and in the medium with... 

Orientational polarization can occur in substances composed of molecules that have permanent electric dipoles. The alignment of these dipoles depends on temperature and leads to an orientational polarizability per molecule a = fE/3kT, where p is the permanent dipole moment per molecule, k is the Boltzmann constant, and T is the temperature. 

This equation shows that m is proportional to the field E. The orientation polarizability is defined by m = from Eq. (26.18), we obtain... 

The total polarizability of any molecule is the sum of the distortion polarizability and the orientation polarizability, Eq. (26.13). Thus we have... 

Free energy of hydration studies of simple cations have shown that the Born correction predicts only about half the correction expected, based on molecular simulations with different cutoff radii.The orientational polarizability of water in the vicinity of a simple cation has been studied to assess the conditions under which Born-like behavior can be expected. 

Molecules with polar groups possess a permanent dipole moment pp. In these molecules, a static electric field produces an orientation polarizability, in addition to induced atomic or electron polarization i.e., the most probable rest position for the permanent dipole lies preferentially in the direction of the field. Molecules with permanent dipoles thus often store more electrical energy than those with induced dipoles. 

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