Dipole shift

For the three smallest islands - containing 7, 19 and 37 CO molecules - the full vibrational eigen value problem was solved to yield dipole shifts relative to the singleton of 12, 17 and 20 cm-1 respectively. In addition, it was found that for these small islands certain vibrational modes other than the fully in-phase mode have non-zero intensity, and in each case bands having an intensity of a few percent of the major band s appear at lower frequency. 

While none of the calculated quantities exhibits an overall monotonic trend with increasing polarity, they all show the same nonmonotonic pattern, in which the trend of dipole shifts is inversely correlated with that for HDA, p,12, and AEn. A key feature governing this behavior is the fact that inertial solvation is equilibrated to the site with less access to solvent (i.e., AC, the site of the initial state hole) in comparison with the more accessible ABP site (where the charge resides in the final state). As a result, there is a mismatch in dipolar solvation in the vertical CSh absorption, such that within the solvent sequence (e0 = 1-8, 7.0, and 37.5), increasing the polarity actually decreases the degree of charge localization (i.e., smaller A/xn and A/zda, an effect dominated by the oxidized D site in the final state), and hence increases the D/A coupling (as reflected in HDA and also p.n). 

It is usually the case that there is a considerable contact shift on the resonances of nuclei of atoms in the first coordination sphere of Ln(III) ions. The contact shifts can be separated from the dipolar shifts by quite simple procedures15,16) involving the study of complexes of the ligand with different Ln(III) assuming that the dipole shifts have axial symmetry, Fig. 2. The deduced contact shifts are quite useful in that they show which atoms are directly bound to Ln(III) in the complexes. We shall not concern ourselves further with contact terms in this article as no detailed structural information is available from them. The coordination sphere is usually generated by the searches using only dipolar shift and relaxation data. 

Fig. 18. FT-RAIRS spectra of CO adsorbed at 300K on IML and 20ML films of palladium deposited by metal vapour deposition on TiO2(110) [56]. The switch from a local titania dielectric (transmission band) to that of the metal (absorption band) takes place at about lOML of palladium. The singleton frequency and the coverage dependent dipole shift are similar for both palladium layers indicating little perturbation of the CO adsorption behaviour on the palladium by the Ti02(l 10) substrate.

When the multistate GMFl transformation as defined here yields more than one diabatic state localized on the same site, we impose the additional condition that a block of the diabatic Flamiltonian associated with a single site be diagonal, thus yielding states diabatic in the GMFl sense with respect to inter-site coupling, but locally adiabatic within each site or local region [30]. Clearly, this approach rests on a distance scale separation D and A sites of small spatial extent relative to da-In a multistate situation, the GMH analysis employs the component of each dipole vector in the mean direction defined by the adiabatic dipole shifts for the various electron transfer processes of interest. 

Figure 7.8 Absolute value of strength function for Na44 " excited with an initial dipole shift at two different amplitudes, as indicated by the excitation energies. The case = 0.6 eV stays in the linear regime whereas = 10.0 eV is in the multiplasmon regime (about 3-4 plasmon excitation). The strength function from linearized TDLDA (= RPA) is also drawn for comparison. The RPA peaks have been given a width of 0.04 eV for smooth representation and better comparison with the TDLDA results. All results have been normalized to the same maximum peak height for better comparison...

The numbers in parentheses are the leading terms in the expansion about the molecular centers of mass for the electrostatic contribution this is the resonant dipole-dipole splitting, for the induction contribution this is the dipole-induced dipole shift. 

Next we have calculated the frequencies and the intensities of the dimer vibrational transitions in the range of the 1/3 vibrations of SFe and SiF4 and the 1/4 vibration of SiH4. The force fields used for the monomers are given in Ref. 8. We have analyzed the various contributions to the splitting and shifts of the monomer frequencies, and we have investigated the orientational dependence of each contribution, as well as the orientational dependence of the dimer transition strengths. From the results in Table 2 we conclude that the electrostatic contributions are dominant in all cases. As explained in Section 2, the electrostatic dipole-dipole shifts (indicated in parentheses) are —2A, — A, A and 2A, for all dimers, independent of the monomer orientations. Also the dipole-induced dipole shifts have constant ratios —4 — 1 — 1 —4, independent of the monomer orientations. 

At the dipole site, zim Zom - -3.425, a a while in the atomic vacancy or ion positions, zim < zom — 1-75 Bohr radii due to the strong localization of electrons at the surface. The SPB increases its degree of saturation with the outward shift of the image plane zo- This means that formation of metal dipoles shifts the electron clouds outwardly and enhances the density of the shifted electronic clouds. 

Permanent dipole terms have been added to rod-shaped GB models [51-55] and the important modifications observed for the molecular organisation have been studied. The effect of a dipole on mesophase stability depends on its position, orientation and strength, so that a detailed analysis is required. In general a terminal axial dipole shifts the nematic-isotropic transition to higher temperatures [51] and a central axial dipole stabilises the smectic [52]. Particularly noticeable is the formation of dipolar domains for GB particles with an axial near terminal dipole [52], leading to a striped dipolar organisation, the so-called smectic A phase [58]. GB molecules with transverse dipoles [55] give rise to chains of dipoles in a plane perpendicular to the director, similarly to what has been found in hard spherocylinders with a transverse dipole [57]. 

The large resonance-induced dipole shifts found in 1/0-6.3 are precisely those due to NBO donor-acceptor delocalizations studied previously (cf. Figs. 5.2 and 5.4). Although the quantity of charge transferred in such delocalizations appears modest, the transfer distance is appreciable, and such distance-dependence is directly sampled by the dipole operator (6.17) and integral (6.16). Thus, some of the most striking consequences of nonclassical resonance-type delocalizations are to be found in dipole moments and transition values (spectral intensities) that are often portrayed superficially as classical electrostatic in nature. 

Characteristic dipole shifts and vibrational intensity enhancements associated with intermolecular charge transfer, investigated by DIPOLE analysis (Section 6.2). 

Pervushin K, Riek R, Wider G and Wuthrich K 1997 Attenuated T relaxation by mutual cancellation of dipole-dipole coupling and chemical shift anisotropy indicates an avenue to NMR structures of very... 

It has already been said that the merits of a method for charge calculation can be assessed mainly by its usefulness in modeling experimental data. Charges from the PEOE procedure have been correlated with Cls-ESCA shifts [28], dipole moments [33], and NMR shifts [34], to name but a few. 

Semiempirical methods are parameterized to reproduce various results. Most often, geometry and energy (usually the heat of formation) are used. Some researchers have extended this by including dipole moments, heats of reaction, and ionization potentials in the parameterization set. A few methods have been parameterized to reproduce a specific property, such as electronic spectra or NMR chemical shifts. Semiempirical calculations can be used to compute properties other than those in the parameterization set. 

The conformational characteristics of PVF are the subject of several studies (53,65). The rotational isomeric state (RIS) model has been used to calculate mean square end-to-end distance, dipole moments, and conformational entropies. C-nmr chemical shifts are in agreement with these predictions (66). The stiffness parameter (5) has been calculated (67) using the relationship between chain stiffness and cross-sectional area (68). In comparison to polyethylene, PVF has greater chain stiffness which decreases melting entropy, ie, (AS ) = 8.58 J/(molK) [2.05 cal/(molK)] versus... 

A solubihty parameter of 24.5-24.7 MPa / [12.0-12.1 (cal/cm ) ] has been calculated for PVF using room temperature swelling data (69). The polymer lost solvent to evaporation more rapidly than free solvent alone when exposed to air. This was ascribed to reestabUshment of favorable dipole—dipole interactions within the polymer. Infrared spectral shifts for poly(methyl methacrylate) in PVF have been interpreted as evidence of favorable acid—base interactions involving the H from CHF units (70). This is consistent with the greater absorption of pyridine than methyl acetate despite a closer solubihty parameter match with methyl acetate. 

Compound CAS Registry Number Boiling point, °C Density at 20°C, g/cm Dipole moment, 10-"° Cm Index of refraction, < PR nmr Parameters chemical t shift, ppm ... 

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