Optimization of spectra

2001 cf Manceau et al. 1998, Fig. 2). Z-Y is the plane onto which the sample hes, with the X-ray beam impinging along X and hnearly polarized on X-Y a is the incidence (rotation) angle between the electric field vector e and Y. 

For a perfectly random distribution of very small crystals (powder) there would be no angular variation effect on the experimental XAS spectra however, for a fully oriented crystal structure such as that of a mica blade lying flat on the sample-holder, the amplitude of the scattered photoelectron wave depends on the angle a between the 

Mottana et al. (in preparation) operated at SSRL at the 3-3 beamline (Hussain et al. 1982 Cerino et al. 1984), which is equipped with a double-crystal monochromator made 

Changes with orientation are also clearly evident in the XANES spectra of a number of di- and tri-octahedral micas and one brittle mica, respectively at the Mg (phlogopite Fig. 9), Si (muscovite Fig. 10, and tetra-ferriphlogopite Fig. 11), K (muscovite Fig. 12), and Fe (clintonite Fig. 13, and tetra-ferriphlogopite Fig. 14) K edges. Such changes 

To summarize, in order to obtain XANES spectra that may be meaningfully compared, we recommend orienting the sample, when a single crystal, always at the same angle of rotation a = 54.7°. This is essentially the same conclusion reached by Manceau et al. (1998) for the self-supporting clay films they experimentally investigated by 

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