Spectroscopically effective radius

The radius thus calculated from the theory of Smith and Symons does not correspond to any known property of halide ions. However, when the acceptable physical model of Franck and Platzman is combined with the concept of a variable radius, as proposed by Smith and Symons, both absolute value and environmental effects can be accounted for. This was done in the theory of Stein and Treinin (18, 19, 47), using an improved energetic cycle to obtain absolute values of r, the spectroscopically effective radius of the cavity containing the X ion. These values were then found to correspond to the known partial ionic radii in solution, as did values of dr/dT to values obtained from other experiments. The specific effects of temperature, solvents, and added salts could be used to differentiate between internal and such CTTS transitions where the electron interacts in the excited state strongly with the medium. These spectroscopic aspects of the theory were examined later in detail and compared with experiment by Treinin and his co-workers (3, 4, 32, 33, 42,48). 

So it would seem that the lone carbon atom in these molecules may adopt a number of geometries with a range of spatial requirements. It remains to be seen whether or not there is any correlation between the effective radius of the carbon atom and its chemical or spectroscopic properties. 

Quantum confinement exhibits novel spectroscopic effects in senuconductors and quantum dots, where the carriers are pinched into a dimension smaller than the Bohr exciton radius. As Zych has pointed out [192], the situation is different in insulators where electronic states are strongly localized. Nevertheless, there have been reports in the literature of quantum confinement effects of Ln " doped into sesqiuoxides, as evidenced by excitation or emission spectra. The spectroscopic effects are very minor so that other causes due to impurities, phase changes, or physical effects such as scattering, certainly play an important role. In particular, combustion syntheses produce variable spectroscopic results, particularly when non-stoichiometric ratios are employed [193]. Zych has ruled out quantum confinement effects for insulators doped with lanthanide ions, at least down to 6 nm. 

The Mossbauer effect involves the resonance fluorescence of nuclear gamma radiation and can be observed during recoilless emission and absorption of radiation in solids. It can be exploited as a spectroscopic method by observing chemically dependent hyperfine interactions. The recent determination of the nuclear radius term in the isomer shift equation for shows that the isomer shift becomes more positive with increasing s electron density at the nucleus. Detailed studies of the temperature dependence of the recoil-free fraction in and labeled Sn/ show that the characteristic Mossbauer temperatures Om, are different for the two atoms. These results are typical of the kind of chemical information which can be obtained from Mossbauer spectra. 

For a same molecular ratio of aqueous NaY solutions (Y = OH, Cl), experimental data underlines specific effects of nascent OH radicals on transient UV and near-IR electronic configurations. Complex investigations of PHET reactions in the polarization CTTS well of aqueous CT and OH ions are in progress. We should wonder whether a change in the size of ionic radius (OH -1.76 A vs Cl" 2.35 A) or in the separation of the energy levels influence early branchings of ultrafast electronic trajectories. A key point of these studies is that the spectroscopic predictions of computed model-dependent analysis are compared to a direct identification of transient spectral bands, using a cooled Optical Multichannel Analyzer... 

The quantities determined directly by the spectroscopic analysis as performed for hot stars are effective temperature Tef f surface gravity g and element abundances. Of course, this is not sufficient to place a star in the HR diagram. This is possible only with further knowledge of either luminosity, radius, mass or distance of the star. However, uncertainties in these quantities (which are usually much larger than the uncertainties in Te and g) directly translate into the HR diagram. On the other hand, theoretical evolutionary tracks can be easily expressed in terms of Teff and g without loss of precision. It is therefore good practice to discuss the results of spectroscopic analyses directly in a (log Te -log g) diagram as we shall do in this paper. 

Small metal particles on the nanometer dimension are of particular interest regarding their solid-state properties as well as their important application as catalysts. Such particles offer a useful model allowing the study of structural effects with relevance for a variety of applications in chemistry and physics. The key point of interest lies in the fact that such particles often possess very different and sometimes novel properties compared to those of bulk materials, i.e., their physical properties (spectroscopic, electronic, magnetic) differ from those of the bulk phase and are particle size-dependent [68]. One such property concerns the variation in the electrochemical redox potential between metals in a dispersed and bulk state, as was shown by Plieth [69], when he demonstrated that the redox potential depended on the radius (r) of a metal particle on nanometer dimension (the radius was assumed to vary from 1 to lOnm) according to the following equation ... 

Zwitterionic PLCllu 15-/>PLLys,5 in water (Fig. lc) can self-assemble into unilamellar vesicles with a hydrodynamic radius of greater than 100 nm (SANS), as shown by Rodriguez-Hernandez and Lecommandoux [24], A change of the pH from 3 to 12 induced an inversion of the structure of the membrane (NMR) and was accompanied by an increase of the size of vesicles from 110 to 175 nm (DLS). Whether the formation of vesicles was controlled by a secondary structure effect or simply by copolymer composition (geometry) remains an open question. Spectroscopic data supporting an a-helical conformation of the polypeptide in the hydrophobic part of the membrane, as speculated by the authors, were not provided. It appears that, however, the peptide segments could be too short to form a stable a-helix. 

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