Re: shape of the instrumental profiles

[Andreas Leineweber]

This is of course a largly simplified view, but it can be explained (i) low angles: the receiving slit contribution to the instrumental abberrations (which is constant with 2theta) leads to a convolution of a rectangle (width independent from 2theta) over the other contributions. This leads largely to a shift of the peak-shape on the Gaussian-Lorentzian scale towards Gaussian (if you try to fit a rectangular profile with a pseudo-Voigt function, you get a "sub-Gauss"-case, i.e. eta < 0. (ii) high angles: the wave-length emission function is largely Lorentzian, and contributes with a constant shape but a width proportional to tan(theta) to the overall profile. Since tan(theta) becomes large at high angle, this dominates at high angles. Best regards Andreas Leineweber Angel L. Ortiz wrote: Dear colleagues:   Does anyone know why the instrumental profiles (instrumental resolution) are generally Gaussian for low diffraction angles, whereas turns to Lorentzian for high diffraction angles?.   Any advice is greatly appreciated.   Thanks in advance,   Prof. Angel L. Ortiz -- Dr. Andreas Leineweber Max-Planck-Institut fuer Metallforschung Heisenbergstrasse 3 70569 Stuttgart Germany Telephone: +49 (0)711 689 3365 Telefax: +49 (0)711 689 3312 [EMAIL PROTECTED] http://www.mf.mpg.de/de/abteilungen/mittemeijer/english/index_english.htm