L absorption edges

X-Ray Absorption Spectroscopy. As the excitation energy incident on a sample is increased, sharp rises in absorption occur at the K, L,..., absorption edges where the energy just matches that required for ionization by ejection of an electron from the K, L,. .., sheUs. These energies are characteristic for each element. The absorption foUows Beer s law (eq. 1), which in this region is usually written as A( A) = )px where p is the density,... 

Figure 5. X-ray absorption spectrum of a silica supported platinum-iridium catalyst at 100 K in the region of the L absorption edges of platinum and iridium. Reproduced with permission from Ref. 13. Copyright 1982, American Institute of Physics.

Figure 1. The L-absorption edges of 2.5 urn thick Ft foil at 298 K. The zero of energy is defined by the Ft Ljjj edge at 11,563.7 eV.

A study of the area of the L absorption edge resonance shows a correlation with chemical activity. This implies a correlation with the number of d-band vacancies. This occurred when Pt oxide was reduced by hydrogen or when the particle size was decreased (13). 

Figure 2.73 (a) The X-ray absorption spectrum of copper showing the K- and L-absorption edges, (b) The K.-edge in more detail. From A.R. West, Solid State Chemistry and its Applications, John Wiley and Sons, Chichester (1984). Reprinted by permission of John Wiley and Sons, Ltd. 

Log-log plot of mass absorption coefficient against wavelength for lead showing K and L absorption edges. 

Figure 5.3 K and L absorption edges of tungsten. The absorption of the solid decreases as the energy of the X-rays increases (i.e., as the wavelength decreases), but when the energy exceeds the threshold for a particular excitation process to occur (e.g., the eviction of an Lm electron at 10.2 KeV), the absorption jumps substantially.

Fig. 2. Dispersion of fo + f of europium in EufPhAcAc), at the three L-absorption edges after Lye, Phillips, Kaplan Doniachand Hodgson ). The f"-values were calculated by using the Kramers-Kronig relation (Eq. (17)). The absolute scale (in electrons) relies on values of f and f at CrK, and CuK, which were taken from The International Tables of Crystallography, IV ...

As b" is of the order of 10 ° mm and the wavelength of the order of 10 mm about some hundred atoms should scatter coherently in order give the same intensity contribution as fluorescence. This is shown as a function of the atomic number for resonance scattering at the K- and L, absorption edges in Fig. (10). 

X-Ray Photoelectron Spectroscopy (XPS) of the 3d core level of cerium and X-Ray Absorption Spectroscopy (XAS) of the L... absorption edge of cerium have been used to study Pd/Ce02, Pd-Ce/yA O and Ce/y A O catalysts. The oxidation state of cerium was found to decrease with decreasing amounts of cerium on the surface. It was quite close to III for very low contents of cerium (2-3%). For higher cerium contents the oxidation state was nearer to IV but differences between the two methods were found, owing to the fact that XAS is a volume sensitive probe. The oxidation state of cerium wa also lower for Pd-Ce/yAl-O than for Ce/yAl O, suggesting the formation of Ce OC1, chlorine coming from The precursor salt of palladium. 

Figure 7.14 Difference Fourier map calculated with coefficients (FV hmono f Nvmono) expictj gsiROASLaue ( ) correct hand (b) no hand (c) incorrect hand. The mercury wavelength normalised Laue (3 A) data were selected only if the stimulating wavelength was S1A so as to yield an optimised anomalous dispersion signal from the Hg L absorption edges. From Helliwell et al (1989a) with the permission of the American Institute of Physics.

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