Bulk susceptibility term

The reference compound can be added to the sample solution (internal reference) or kept separate from the sample in a sealed capillary (external reference, Fig. 2.36). If an external reference is necessary, a correction term accounting for the difference between the bulk susceptibilities of reference ( R) and sample solution ( s) must be added to the observed shift, dob5 ... 

Table 3.1. Composition of the parameters, a, b, and c in terms of the surface and bulk susceptibility elements. P-polarized ( ) or s-polarized ( O) fundamental field, i = (x,y)...

We consider now the NLO response of a molecule to an electric field. The resulting equations will be found to be analogous to the ones derived for a bulk medium. Instead of bulk susceptibilities however, molecular polarizabilities of nth order appear. For the latter, by convention, the lower-case Greek letters in ascending order (a, 3, y,. ..) are used. Again, an electric field of the form defined in (16) is used. Similar to the macroscopic polarization (17), the expression (33) for the molecular dipole moment p t) contains linear and non-linear terms. 

The relatively small changes in chemical shift with pressure can be qualitatively explained in terms of changes in bulk susceptibility as most spectra in SCFs are obtained without internal lock. Large chemical shift ranges are a characteristic of metal NMR spectroscopy, and the changes observed on changing temperature, pressure or solvent are no more exaggerated in supercritical solvents than those observed with conventional solvents. 

At this juncture we have in place a formalism that fully accounts for the refractive and dissipative modifications of the fundamental fields due to the dispersive electronic properties of the optical medium. This has been achieved not by any phenomenological or other ad hoc approach, but from first principles, using the theoretical methods of molecular QED. As a result, the necessary local field corrections in condensed media naturally emerge from the detailed form of the auxiliary field operators, obviating the need to encompass them indirectly in terms of macroscopic bulk susceptibilities, as is necessary in the semiclassical theory. 

Prof. Levitt uses the term demagnetization field effect (as will we) but terms such as bulk nuclear-paramagnetic-susceptibility-induced transients, dipolar field, or bulk susceptibility effects have also been used. 

There are of course similar terms for the y,z axes, and in the absence of cubic symmetry, anisotropy arises because the values of a and X, and hence of the parameter a may be different for the various axes. An advantage of this method of measuring the Van Vieck moment, under conditions where inequivalent ions are present, is that the contribution from each type of ion can be found, where a measurement of the bulk susceptibility gives only the sum of all the individual contributions. 

Of the four nonlinear crystal types investigated in this paper (figure 20), bulk KNbOs was superior in terms of generated blue average power (11.8 mW) and generated beam quality. KNbOs is also less susceptible to the observed saturation and subsequent decrease in SHG efficiency observed in both waveguide crystals. 

The negative coefficient of E° and Ef indicates an enhancement of activity with an increase of steric bulk. Especially, the variation in activity against barnyard grass is mainly governed by steric factors. If steric bulkiness prevents the proper fit with the target site, these results mean that it inhibits the interaction with some enzymes which participate in the detoxication process(es) in the plant body. The negative slope of the cr term in Eq. 15 and 16 coincides with this view, i.e. a molecule with a more electron-withdrawing substituent becomes more susceptible to a hydrolytic attack. 

The interest in semiconductor QD s as NLO materials has resulted from the recent theoretical predictions of strong optical nonlinearities for materials having three dimensional quantum confinement (QC) of electrons (e) and holes (h) (2,29,20). QC whether in one, two or three dimensions increases the stability of the exciton compared to the bulk semiconductor and as a result, the exciton resonances remain well resolved at room temperature. The physics framework in which the optical nonlinearities of QD s are couched involves the third order term of the electrical susceptibility (called X )) for semiconductor nanocrystallites (these particles will be referred to as nanocrystallites because of the perfect uniformity in size and shape that distinguishes them from other clusters where these characteriestics may vary, but these crystallites are definitely of molecular size and character and a cluster description is the most appropriate) exhibiting QC in all three dimensions. (Second order nonlinearites are not considered here since they are generally small in the systems under consideration.)... 

The magnetic susceptibility is thus a temperature-dependent property of a bulk substance. It is meaningless to specify the susceptibility of a single molecule or complex ion. For convenience, inorganic chemists prefer to answer the question How paramagnetic is this substance in terms of the magnetic moment peff defined by the relation ... 

Solvent effects on nuclear magnetic resonance (NMR) spectra have been studied extensively, and they are described mainly in terms of the observed chemical shifts, 8, corrected for the solvent bulk magnetic susceptibility (Table 3.5). The shifts depend on the nucleus studied and the compound of which it is a constituent, and some nuclei/compounds show particularly large shifts. These can then be employed as probes for certain properties of the solvents. Examples are the chemical shifts of 31P in triethylphosphine oxide, the 13C shifts in the 2-or 3-positions, relative to the 4-position in pyridine N-oxide, and the 13C shifts in N-dimethyl or N-diethyl-benzamide, for the carbonyl carbon relative to those in positions 2 (or 6), 3 (or 5) and 4 in the aromatic ring (Chapter 4) (Marcus 1993). These shifts are particularly sensitive to the hydrogen bond donation abilities a (Lewis acidity) of the solvents. In all cases there is, again, a trade off between non-specific dipole-dipole and dipole-induced dipole effects and those ascribable to specific electron pair donation of the solvent to the solute or vice versa to form solvates. 

In order to analyse bulk polarity effects it is common to represent the electrostatic response of the solvent in terms of the polarization function P. This vectorial function in fact can be directly connected to any electric field (here that produced by the solute) through a single quantity, the susceptibility x> or equivalently the permittivity e [9],... 

Here Pind is the induced dipole moment per unit volume, and X X and X are the first-, second-, and third-order electric susceptibilities of the sample, where the order refers to the power of electric field (not of X). Equation (1) represents the macroscopic (bulk) form for the polarization in terms of single molecule properties, the induced dipole moment per molecule is written as... 

It was assumed that OsO,F, would be colourless and diamagnetic and phjrsically similar to OsOF, and OsF,. The infrared spectra of osmium oxide pentafluoride samples taken from a variety of preparations were identical with one another. The entire product from one oxyfluorination of osmium metal was subjected to infrared examination. The bulk of the sample in a Monel trap, was isolated from the gas cell by a Hoke valve. After each vapour sample had been scanned it was discarded and a new sample of vapour admitted. This was repeated exhaustively. All the spectra were interpretable in terms of OsF OsOF OsO and traces of HF, CF, SiF and CO,. Two independent magnetic measurements on samples of OsOF one from an oxjrfluorination of the metal and the other from the fluorination of the dioxide gave magnetic susceptibility values equal within the usual experimental uncertainty. Furthermore the magnitude of the susceptibility was consistent with pure OsOF,. 

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