Low-energy spectra

Because of limitations of computer resources and of research personnel, c lcula jgns were previously performed for only about 25 nuclei ranging from 1 C to °Pu. It was shown [KUM84, and previous references cited there] that the major trends of the low-energy spectra and electromagnetic moments could be reproduced for the first time without any local parameters. More recently, the model has been extended in several directions. Because of space and time limitations, only three of these are discussed below. 

Figure III-2 Reflectance spectra of PPy-PF in the metallic regime (solid line) and in the insulating regime (dotted line) measured at room temperature. The inset shows the low-energy spectra (hv < 0.5 eV) with expanded scale. (Taken from ref. 67)...

Bolded masses represents ions unique to the low energy spectra. An asterix denotes the base peak. Other references 180, 183, 184. 

Figure 5. Calculated spectra of the pure components, as determinedfrom SVD analysis. The low-energy spectra (500-1200 nm) were recorded at ten times the concentration of 1, relative to the concentration for the high-energy spectra accounting for the discontinuity at 500 nm. (Reproduced with permission from PhD dissertation, Duquesne University.)...

An Important feature of this application of low energy electrons lies In the rapid Increase In electron stopping power (dE/dx) with decreasing energy.(7) If such low energy spectra can be produced... 

Figure Bl.25.2 shows the XPS spectra of two organoplatinum complexes which contain different amounts of chlorine. The spectrum shows the peaks of all elements expected from the compounds, the Pt 4f and 4d doublets (the 4f doublet is iimesolved due to the low energy resolution employed for broad energy range scans). Cl 2p and Cl 2s, N Is and C Is. Flowever, the C Is caimot be taken as characteristic for the complex only. All surfaces that have not been cleaned by sputtermg or oxidation in the XPS spectrometer contain carbon. The reason is that adsorbed hydrocarbons from the atmosphere give the optimum lowering of the surface free energy and hence, all surfaces are covered by hydrocarbon fragments [9].

The UV spectra of thiirane 1-oxide and (15,25)-(+)-2-methylthiirane 1-oxide show a broad maximum at about 205 nm (e —23 000). The latter shows a positive Cotton effect at low energy followed by a negative effect at high energy. The lowest excited states of thiirane 1-oxide involve excitations from the two lone pairs of the oxygen atom (79G19). 2,3-Diphenylthiirene 1-oxide and 1,1-dioxide show absorption due to the 1,2-diphenyl-ethylene chromophore. 

NRA exploits the body of data accumulated through research in low-energy nuclear physics to determine concentrations and distributions of specific elements or isotopes in a material. Two parameters important in interpreting NRA spectra are reaction Qvalues and cross sections. 

It should be noted that low-loss spectra are basically connected to optical properties of materials. This is because for small scattering angles the energy-differential cross-section dfj/dF, in other words the intensity of the EEL spectrum measured, is directly proportional to Im -l/ (E,q) [2.171]. Here e = ei + iez is the complex dielectric function, E the energy loss, and q the momentum vector. Owing to the comparison to optics (jqj = 0) the above quoted proportionality is fulfilled if the spectrum has been recorded with a reasonably small collection aperture. When Im -l/ is gathered its real part can be determined, by the Kramers-Kronig transformation, and subsequently such optical quantities as refraction index, absorption coefficient, and reflectivity. 

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