Polarizabilities measurements

Miller T M and Bederson B 1988 Electric dipole polarizability measurements Adv. At. Mol. Phys. 25 37... 

Again we digress to discuss soft and hard (11). It has been said that polarizability measures softness and that the permanent charge-cloud distortion is responsible for (b)-class behaviour. Unfortunately polarization energies of this kind work in two ways — they generate (i) (b)-class behaviour due to anion polarizability but (ii) (a)-class behaviour due to the cation polarizability. Thus if softness and polarizability are related they are not necessarily related to (b)-class behaviour. Moreover on the basis of polarizability of this kind there can be no preferential soft-soft or hard-hard interaction. 

The experimental values of the polarizability a = V2 (2a + of 1 and its anisotropy Aa = oL.-oL x 5.50 and -0.74 which have been obtained by extrapolating polarizabilities measured at optical frequencies to their static limits Amos and Williams calculated for a and Aa 5.03 and -0.67 at the HF/[5s3p2d/3slp] level, which are about 10% too small, typical of HF/large basis set calculations. As can be seen from Table 23, a = oiyy (components in the ring plane) is larger than a (perpendicular to the ring plane). Since an... 

In 1994, a review on the further development and improvement of the n scale was given by Laurence, Abboud et al. [227], They redetermined n values for a total of 229 solvents, this time using only two (instead of seven) solvatochromic nitroaromatics as indicator compounds, i.e. 4-nitroanisole and A,A-dimethylamino-4-nitroaniline, for good reasons see later and reference [227] for a more detailed discussion. A thermodynamic analysis of the n scale [and the t(30) scale] has been reported by Matyushov et al. [228]. Using six novel diaza merocyanine dyes of the type R-N=N-R (R = N-methylpyridinium-4-yl or A-methylbenzothiazolium-2-yl, and R = 2,6-disubstituted 4-phenolates or 2-naphtholate) instead of nitroaromatics as positively solvatochromic probe compounds, an analogous n azo scale was developed by Buncel et al., which correlates reasonable well with the n scale, but has some advantages for a detailed discussion, see references [333], Another n scale, based solely on naphthalene, anthracene, and y9-carotene, was constructed by Abe [338], n values are mixed solvent parameters, measuring the solvent dipolarity and polarizability. The differences in the various n scales are caused by the different mixture of dipolarity and polarizability measured by the respective indicator. The n scale of Abe is practically independent of the solvent dipolarity, whereas Kamlet-Taft s n and Buncel s n azo reflect different contributions of both solvent dipolarity and polarizability. 

Polarizabilities measure the response of ions or atoms to an electric field. Electronic polarizabilities, a, arise from deformation of the electron cloud relative to the nucleus and are given by the Lorenz-Lorentz equation ... 

The "A" parameter can be obtained from atomic polarizability measurements or can be calculated quantum mechanically. The "B" parameter is typically derived from crystallographic data so as to reproduce observed average contact distances between different kinds of atoms in crystals of various molecules. 

The empirical treatment of solvent-solute interactions by means of the jt parameters was re-examined 15 years after their introduction16. It was concluded that AAAAdimethyl-4-nitroaniline (7), not used in the original introduction of the jt scale, is superior to N,N-diethyl-4-nitroaniline (5) employed originally, since the former is not appreciably affected by differences in band shapes in different solvents as the latter is, due to vibrational structure. An extensive table of v(7) in 229 solvents and the gas phase was provided (and found well correlated linearly with v(2)). New jt values were obtained for several solvents that differed somewhat from the previously established values4,7. The wavenumbers (in cm-1) of 7 were shown to depend on the polarizability (measured by the refractive index n) and the polarity (measured by the relative permittivity e) of the solvent for 66 non-aromatic solvents as follows (equation 10) ... 

Polarizability measures the response of an ion or molecule to an electric field and is expressed in units of volume, typically 10 cm or A Polarizability increases with atomic or ionic radius it depends on the effectiveness of nuclear screening and increases as each valence shell is filled. Table 1.4 gives the polarizability values for the second-row atoms and some ions, molecules, and hydrocarbons. Methane is the least polarizable hydrocarbon and polarity increases with size. Polarizability is also affected by hybridization, with ethane > ethene > ethyne and propane > propene > propyne. 

David R. Bates and George A. Victor Alexander Dalgamo Contributions to Atomic and Molecular Physics Neal Lane Alexander Dalgamo Contributions to Aeronomy, Michael B. McElroy Alexander Dalgamo Contributions to Astrophysics, David A. Williams Dipole Polarizability Measurements, Thomas M. 

The yariation in catalytic function with increasing oxygen coyerage is in excellent agreement with surface characterization by molybdenum core leyel shifts and surface polarizability measurements. Clearly the physical measurements were performed on the actual catalytically actiye sites, and the nature of the actiye sites has been established. The catalytic results combined with the spectroscopic data also serve to calibrate the minimum molybdenum oxidation state required for acid catalyzed C-C bond breaking and formation of a secondary carbenium ion, namely. Mo(IV). 

The incongruous patterns can be explained with the aid of the HSAB principle. From polarizability measurements (131, 132), it may be concluded that the softness scale is Br > CN > Cl . The soft carbon nucleophile of the enamine systems seeks out the softer acid. 

Kadar-KaUen MA, Bonin KD (1994) Uranium polarizability measured by light-force technique. Phys Rev Lett 72 828-831... 

According to (2.12) the optical anisotropy As = njf — n is completely defined by the anisotropy of polarizability, measured parallel and perpendicular to the long molecular axis A7. The values of optical anisotropy increase [14,28] with ... 

Polarizability measures how easily the distribution of the electrons around an atom or molecule can be deformed by an appUed electric field. 

TABLE 10.1 First ionization potentials (lEj), permanent electric dipole moments (/t), and polarizabilities (a) of selected atoms and molecules. Polarizabilities for non-spherical tops vary with choice of axis, and only an average value, (a — 2a j ) /3, is given a and a are the polarizabilities measured parallel and perpendicular to the principal rotation axis, respectively. Lennard-Jones parameters (e and R ), when provided, are for the dimer of the indicated molecule. 

This polarizability corresponds to the isolated molecular polarizability normalized over the mean field interaction present in the liquid. It can be substantially different from the molecule polarizability measured in the gas phase. 

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