Dear All,
I have a diffraction profile which spans 5-160 degrees. My problem is
getting an adequate fit for four or five peaks which lie in the range 7-20
degrees. I have split my data into two histograms (5-20 and 20-160 deg) to
try and alleviate the problem, and although the fit is better it remains
imperfect. Unfortunately, the problem-peaks are the most important part of
the data profile - I have an occupancy factor which is sensitive only to
these peaks. I believe a peak-profile based on Pearson-VII rather than
Pseudo-Voigt would resolve the problem. What I would like to know is:
(a) Does a PVII profile function exist for constant-wavlength data within
GSAS, or are all the functions currently available based on the
Pseudo-Voigt? I can't believe I am the only one to suffer from this form
of asymmetry and therefore have the sneaking suspicion that perhaps I'm not
using the available peak-shape functions to their full potential.
(b) Perhaps the functions available for TOF data may be of use. Is there
any way I can force GSAS to use the peak-shape functions normally reserved
for TOF data (without converting my 2-theta data to some arbituary TOF scale)?
(c) Alternatively, is it possible to enter integrated intensities rather
than using the data profile. I could then use another software package it
fit the data using PVII and extra intergrated intensities. This
unfortunately removes some of the beauty of the Reitveld method.
Thanks in advance,
Colin Lobban.
