Polarisability xenon

Throughout we have considered only the portion of the mole refraction produced in the outermost shell. In the case of xenon one finds by our methods that as much as 4 per cent, of the total mole refraction is due to the N shell accordingly our values of SK for the 0 electrons would be decreased by about 0-1 on making this correction. The values of R for ions would in most cases not be changed materially by the explicit consideration of the polarisation of inner shells, and so the less complicated treatment of this paper has been adopted. 

The NMR chemical shift of I29xe adsorbed on molecular sieves reflects all the interactions between the electron cloud of the xenon atoms and their environment in the intracrystalline void volume [1]. This nucleus therefore proved to be an ideal probe for investigating various zeolitic properties such as pore dimensions [2, 3], location of the countercations [4, 5], distribution of adsorbed or occluded phases [6-8] and framework polarisability [8, 9]. 

NaY zeolite at 60.1 ppm. The image was obtained for a 3mm slice with full chemical shift imaging (note that for thermally polarised Xe this type of imaging experiment would be far more demanding in terms of experimental time even than chemical shift resolved imaging, as practiced for the Aerogel samples[30]), and was obtained in 30 min. Thus, the improvement in imaging with HP xenon over thermally polarized xenon is impressive, and indicates that there are real prospects for applications in the characterization of materials. 

Equation (2.35), known as the Lorenz-Lorentz relation, provides a method of calculating the molecular polarisability from a macroscopic, observable quantity, the refractive index. We must make the proviso that we stay away from any resonant absorption frequency, where the refractive index is anomalously high. If the refractive index refers to optical frequencies, the polarisability a will be purely electronic in origin. In practice, electronic polarisabilities derived in this way are remarkably insensitive to temperature and pressure, even for highly condensed phases in which intermolecular forces must be large. This is illustrated for the particular case of xenon in Table 2.1. 

The experimental arrangement used by Granitza et al. (1993) in their study of spin effects in (e,2e) collisions on xenon is shown in fig. 2.17. The polarisation analysis of the incident beam was in this case carried out with a spherical mini-Mott detector, which is also shown in the figure. 

CD is an excellent method for determining the secondary structure content of proteins in their native state, but it is limited by the fact that much of the information is located at wavelengths (below 200 nm) where the light output from conventional Xenon lamps diminishes markedly. In contrast, the flux obtained from synchrotron light remains high at these wavelengths. Also, the inherent polarisation of synchrotron radiation makes it the ideal light source for CD experiments. 

Hydrates and deuterates have, however, been made by compressing the inert gases with water and DgO. Those formed by the heavier elements are the most stable and contain six HgO or DgO molecules to one inert gas atom, as in Xe.GHgO where the xenon atom is evidently polarised by the strong dipole. This thesis is supported by the increase in water-solubility down Gp. O ... 

The large positive shift and the parabolic behaviour of the 5 = f(N) curves in the case of divalent cations was attributed first by Fraissard at al. [2] to the high polarisability of xenon and the distortion of the xenon electron cloud by the strong electric fields created by the 2+ cations. Later, Cheung et al. [5] proposed a model to explain the strong adsorption of xenon in zeolites with 2+ cations (Ca2+, Mg2+, Ba2+). It consists in extending the electron attraction described above to the point where an electron is transferred from the xenon to the cation. This model suggests that a partial bond between the xenon atom and the 2+ cation is formed by donation of a xenon 5p electron to the empty s-orbital of the 2+ cation. 

In its simplest form the exciting system will consist of a source, illumination optics, filter and polariser, and the intensity-measuring system will consist of an analyser, collection optics, filter and detector. The source of ultraviolet light is usually a mercury or xenon arc and the filter on the source side of the specimen selects from its output a narrow band of wavelengths near the peak of the absorption spectrum of the particular fluorescent molecule in use. The illumination optics should transmit the light as a fairly parallel beam to the specimen, so that it can be given a... 

Fig. I. Apparatus used to make polarised fluorescence intensity measurements from the top (a), the cell compartment (bl, and from the side (c). Xenon arc (Xe), monochromator (M), lens (L). filter (Fi), polariser (Pi), outside shell (OS), inside shell (IS), ciaet (Cu), slide (S), mask (Ma), filter (F2K polariser (Pi), photo-cathode (PC). photomultiplier (PM), power supply (PS), microammeter (A), locking collar (C), scale (Sc), slide holder (H), hole in mask (Ho), movable support (Su).

Xe NMR of adsorbed xenon has proved to be a powerful tool to study the physicochemical properties of zeolites [1]. The highly polarisable Xe atom is very sensitive to its environment, i.e. to the interactions with other chemical species, in particular to the nature and the concentration of coadsorbed molecules. So this technique can be used for the determination of the diffusion coefficients of gases in solids [2]. We have also shown that H NMR imaging can be used for such types of studies [3]. 

Effects other than those of purely viscometric origin were seen to be significant in a schematic study by McHugh and co-workers of the free radical decomposition of cumene hydroperoxide [48], and subsequent oxidation of cumene (isopropyl benzene) [49, 50] in a range of supercritical and liquid solvents. The effective non-catalysed rate coefficients for cumene hydroperoxide decomposition in non-polarisable supercritical fluids (krypton, xenon) were greater than that for non-polar liquid cyclohexane, as expected a priori on the basis of viscosities. Yet, liquid 1-octene and 1-hexanol gave similar... 

The work on heavy atoms has not been restricted to mercury. Studies have been carried out on the inert gases including the 5 Pl and 5 Pi states of krypton and on the 63p2 state of xenon. Because of the difficulty of carrying out polarisation measurements for the UV photons in the decay of these states the angular correlation technique has been used. This restriction reduces the number of parameters which can be obtained since A can no longer be explicitly evaluated. The thre parameters which can be determined are x ", defined as cos x = cos x cos A, and e (with the usual definitions from equation (6)). 

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