[Ifeffit] Re Iffeffit LCF

[fred.mosselmans at diamond.ac.uk]

Dear Niken,

I have had a look and i am afraid there  are some problems, so what follows is not very positive.

I am not sure your normalisation of the dilute samples is very good
i ended up treating each spectrum slightly individually using a post-edge range of about 40-90 and adjusting the pre-edge range depending on the curviness of the pre-edge background. This is not ideal for linear combination fitting but i got spectra that looked like they had an edge step of 1.
So That's fixable.

But  as you noticed the thiophene-10 and thiophene spectra are quite different. (you call it disulfide in your email but there are two thiophene and 1 disulfide spectra in the project.
Ignoring self absorption which might give some relative peak intensity changes, i think this means they aren't the same thing
Preparing your dilute samples some surface oxidation may have occurred
 in thiophene-10 there's a lump at 2481 or so that is bigger and displaced from the pure thiophene sample,  this lump is
quite reminiscent of some sulfate being present - this may be trace  surface amounts, but the experiment will be sampling only about 10 microns worth of real sample so can be very important.
This unfortunately is  i think pretty unrecoverable.

If the samples weren't  well enough mixed and i mentioned earlier you are looking at only about 10 microns worth of powder in the post edge, then of course the sample you looked at is actually an unknown and not a standard, so a good fit  in LCF might be the correct answer.

Regards
Fred


BTW please use Dear Fred, dear professor fred just seems ridiculous to me.



Prof.  J F W Mosselmans
Principal Beamline Scientist I18
Diamond Light Source
Diamond House
Harwell Campus
Didcot
Oxon
OX11 ODE
UK

T 00 44 1235 778568
M 00 44 7785510211
E fred.mosselmans at diamond.ac.uk
F 00 44 1235 778448

Never mind the W it's the tax that counts




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