Dipole moment orientation

The polarization properties of single-molecule fluorescence excitation spectra have been explored and utilized to detennine botli tlie molecular transition dipole moment orientation and tlie deptli of single pentacene molecules in a /7-teriDhenyl crystal, taking into account tlie rotation of tlie polarization of tlie excitation light by tlie birefringent... 

The second problem of interest is to find normal vibrational frequencies and integral intensities for spectral lines that are active in infrared absorption spectra. In this instance, we can consider the molecular orientations, to be already specified. Further, it is of no significance whether the orientational structure eRj results from energy minimization for static dipole-dipole interactions or from the competition of any other interactions (e.g. adsorption potentials). For non-polar molecules (iij = 0), the vectors eRy describe dipole moment orientations for dipole transitions. 

In all cases the dielectric constant used is that of the pure solvent. Neglect of the solute is usually justified by its low concentration and the assumption that any necessary correction would be additive. In at least a few cases where the first two expressions have been employed the linearity of the results is to some extent dependent on how closely the refractive index of the solute meets the conditions n2 = 2.0 or 2.5 a situation not always recognized by the investigators. In one instance attempts have been made to clarify the role of solvent reaction field by examining solutes with different dipole moment orientations relative to the bonds involving coupled atoms. 

At low frequencies, the dipole moments of polymers are able to keep in phase with changes in a strong electric field, and the power losses are low. However, as the frequency is increased, the dipole moment orientation may not occur rapidly enough to maintain the dipole in phase with the electric field. 

UV-Vis absorption spectra show that the polythiophene films exhibit an absorption band at 535 nm, corresponding to the first 7t-7t transition, with a clear vibronic fine structure. This absorption can be attributed to a structure that mainly consists of stacks of nearly coplanar extended chains, with the transition dipole moment oriented along the polymer backbone <2005AM708>. 

The second type of fundamental vibrations involves an oscillating dipole moment, oriented perpendicularly to the unique molecular axis. The corresponding infrared selection rules for the rotational transitions are given by... 

The HC1 molecule Because the electronegativity of chlorine (3.2) is greater than that of hydrogen (2.2), the chlorine is partially negative, and the hydrogen is partially positive. The HCl molecule has a dipole moment oriented as follows ... 

This case is analogous to the water molecule. The polar bonds result in a dipole moment oriented as shown. 

Electric field poling method is widely used for in situ studies ot the dynamics of the dipole moment orientation in amorphous polymers and for poling of new materials, which may potentially possess a great number of defects. This method gives a good efficiency of orientation, but its application is limited only to dipolar molecules. Molecules of the octupolar (threefold) symmetry cannot be poled, as they do not possess a permanent dipole moment. 

To examine the role of the LDOS modification near a metal nanobody and to look for a rationale for single molecule detection by means of SERS, Raman scattering cross-sections have been calculated for a hypothetical molecule with polarizability 10 placed in a close vicinity near a silver prolate spheroid with the length of 80 nm and diameter of 50 nm and near a silver spherical particle with the same volume. Polarization of incident light has been chosen so as the electric field vector is parallel to the axis connecting a molecule and the center of the silver particle. Maximal enhancement has been found to occur for molecule dipole moment oriented along electric field vector of Incident light. The position of maximal values of Raman cross-section is approximately by the position of maximal absolute value of nanoparticle s polarizability. For selected silver nanoparticles it corresponds to 83.5 nm and 347.8 nm for spheroid, and 354.9 nm for sphere. To account for local incident field enhancement factor the approach described by M. Stockman in [4] has been applied. To account for the local density of states enhancement factor, the approach used for calculation of a radiative decay rate of an excited atom near a metal body [9] was used. We... 

We suppose that a small probing held Fj, having been applied to the assembly of dipoles in the distant past (f = —oo) so that equilibrium conditions have been attained at time t = 0, is switched off at t = 0. Our starting point is the fractional Smoluchowski equation (172) for the evolution of the probability density function W(i), cp, t) for normal diffusion of dipole moment orientations on the unit sphere in configuration space (d and (p are the polar and azimuthal angles of the dipole, respectively), where the Fokker-Planck operator LFP for normal rotational diffusion in Eq. (8) is given by l j p — l j /> T L where... 

QSAR studies were carried out to determine what the optimum angle should be for activity. This resulted in an ideal angle for 4> of 30°. A correlation was worked out between the dipole moment orientation, partition coefficient, and activity as follows ... 

If it is assumed that the TDDs are oriented preferentially along a <110> axis, with a C2V site symmetry, the piezospectroscopic results can be explained satisfactorily on the basis of the stress-induced line shifts and polarizations calculated by Kaplyanskii [73], which are discussed in the next section. This led to propose the C2V site symmetry for the TDDs in silicon [137]. In expression (8.15), the non-zero components of the piezospectroscopic tensor for C2v centres, labelled as orthorhombic (or rhombic) I, are Axx (A2), Ayy (A2), Azz Wi) and Axy = Ayx (A3). These orthorhombic I centres have a C2 symmetry axis in the <100> direction and the 1 s —> 2po transitions have their transition dipole moment oriented along this axis for a Is state constructed from a pair of valleys along this axis, while the Is —> 2p transitions have their transition dipole moment oriented in a plane perpendicular to this axis. In a cubic crystal, a C2V centre has a sixfold orientational degeneracy represented by the six diagonals of a cube (see Fig. 8.16a). 

The dispersion effect, produced by the synchronization of the electronic motion in two molecules, which results in momentary dipole moments oriented so as to produce an attraction between the molecules. 

In the histaminic H2 receptor antagonist series, the classical urea-thiourea-guanidine progression was successfully completed by the use of the V-nitro and V-cyanoguanidines and, later on, by l,l-diamino-2-nitroethylene groups (Fig. 13.19). Cyano amidines and carbamoyl amidines were also used, and structure-activity relationship patterns were rationalized in terms of dipole moment orientation of related bioisosteric groups. ... 

FIGURE 15. The rotator plane model of permanent dipole moment variation of the normalized power spectrum of dipole moment orientation fluctuations... 

Figure 13.5. Expected spectral changes predicted as a function of the dipole moment orientation. In the case examined in ref.[7], only (c) can explain the experimental data.

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