Effective dipole moment

Because mole numbers are additive, it follows that the product A. A V will be an additive quantity provided that a for each species remains constant during the course of the reaction. This last condition implies, essentially, that the effective dipole moments and hence the orientation of each species remain constant, which is most likely to be the case at constant film pressure. Then... 

TIk experimentally determined dipole moment of a water molecule in the gas phase is 1.85 D. The dipole moment of an individual water molecule calculated with any of thv se simple models is significantly higher for example, the SPC dipole moment is 2.27 D and that for TIP4P is 2.18 D. These values are much closer to the effective dipole moment of liquid water, which is approximately 2.6 D. These models are thus all effective pairwise models. The simple water models are usually parametrised by calculating various pmperties using molecular dynamics or Monte Carlo simulations and then modifying the... 

The angles ot, p, and x relate to the orientation of the dipole nionient vectors. The geonieti y of interaction between two bonds is given in Fig. 4-16, where r is the distance between the centers of the bonds. It is noteworthy that only the bond moments need be read in for the calculation because all geometr ic features (angles, etc.) can be calculated from the atomic coordinates. A default value of 1.0 for dielectric constant of the medium would normally be expected for calculating str uctures of isolated molecules in a vacuum, but the actual default value has been increased 1.5 to account for some intramolecular dipole moment interaction. A dielectric constant other than the default value can be entered for calculations in which the presence of solvent molecules is assumed, but it is not a simple matter to know what the effective dipole moment of the solvent molecules actually is in the immediate vicinity of the solute molecule. It is probably wrong to assume that the effective dipole moment is the same as it is in the bulk pure solvent. The molecular dipole moment (File 4-3) is the vector sum of the individual dipole moments within the molecule. 

The measurement of change in the surface potentials of aqueous solutions of electrolytes caused hy adsorption of ionophore (e.g., crown ether) monolayers seems to he a convenient and promising method to ascertain selectivity and the effective dipole moments of the ionophore-ion complexes created at the water surface. 

Under such conditions, of course, an essentia] change occurs in the effective dipole moment derivative value along the nuclear coordinate depending upon the entire chain bonding. 

The measured dipole moments for X and XI in different solvents are summarized in Table III. First, the experimental values of p vary from solvent-to-solvent with a trend to higher values for more polar solvents. This may be partly due to the approximations mentioned above. It is also important to note that no attempt was made to account for the nonspherical shape of the dye molecule. We believe that this approximation is justified, since the local field factor used to calculate the hyperpolarizabilities in the EFISH experiment for the product p/J involves similar approximations. Thus, the effective dipole moment determined in these experiments,... 

Fig. 15. The figure on the left shows the time dependence of the current density (A), pholuminescence intensity (B) and the change in photovoltage (C) during the grafting of various diazonium compounds at a potential of —1.2 V. The figure on the right plots the observed photovoltage changes as a function of the calculated effective dipole moment perpendicular to the surface. Reprinted from [90].

In Fig. 6c,d, the calculations were repeated for large pH values, for which most of the basic sites of the surface are associated with OH-, and consequently the association of anions is negligible. In this case, only specific cation effects can be predicted by changes in the effective dipole moment on the surface. As already noted, the interactions between... 

From = iv/(l - 8aecos0/a3) with pv = 1.86 D, we obtain tv = 2.138 D for the effective dipole moment in liquid water from the 298 K bulk dielectric constant. When this is used to estimate the cohesive energy between water molecules in approximately tetrahedral superdipoles at dipole-dipole or O O distances of 2.9 A, the results are about a factor of three too small. The simple dipole-dipole model for water was therefore replaced by a DP multipole-multipole point charge model for hydrogen bonding (c.f., Lih173), and the interactions... 

For a pure dipolar liquid the prefactors m (101) reduce to the Onsager-Lorentz factor (87). We use a double bar ( ) for the effective dipole moment in the energy expression (100). Note that the dipole moment (101) is different from the effective solute dipole moment (102) which results from (84), (88) and (90)... 

The ionization constants of different mono- or polyalkylated pyridazines 4is g ow that the number and position of the alkyl groups affect the basicity of these compounds. Alkyl groups cause an increase in the basicity of pyridazine, due to inductive effects. Dipole moments have also been determined. The NMR spectrum of 3-methylpyridazine shows an ABX system in which —... 

Note that the surface electric field, induced by the incident IR radiation characterizing the thin-film model catalysts, is mainly determined by the NiAl substrate. Consequently, because only the components of the dynamic dipole moment that are perpendicular to the metallic substrate contribute to the SFG signal, the effective dipole moment of tilted molecules is reduced. As a result, the intensity of the signal characterizing tilted molecules is smaller than that of CO molecules oriented perpendicular to the substrate (such as those on the particle top facet). 

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