Re: [Ifeffit] Problem with Hephaestus at Ca L-edges (Matthew Marcus)

Hi Matthew, Jana, I think the Chantler values, especially in Hephaestus, are not particularly robust at the Ca L edges. To be clear, Elam gives L3, L2, and L1 energies as 346.2, 349.7, and 438.4 eV, and the edge jumps as 5.8, 1.4, and 1.1. I believe those edge jumps may have originated from Shaltout -- maybe Bruce can clarify that. The Chantler data from the NIST FFast web page (and in Hephaestus) are quite sparse. This is a definitely a problem for using the anomalous scattering factors near edges. I've talked with Chris Chantler about this a few times over the years. Not too long ago, he sent me data on a finer grid -- but he also told be recently that he hoped to have even better data he could send to me soon (all time-scales here on months-to-years here). I've included the finer data I have from Chantler into Larch. But the results for the Ca L edges are still not encouraging. The attached figure and ASCII data file give the results for mu(E) (gr/cm^2) from Elam and from Chantler. It's hard to see an L2 edge in either, and Chantler does not show an L1 edge. FWIW, the script to generate this is: #################### energies = linspace(300, 500, 101) muca_chantler = mu_chantler('Ca', energies) muca_elam = mu_elam('Ca', energies) newplot(energies, muca_chantler, ymax = 50000, label='Chantler') plot(energies, muca_elam, label='Elam') info_head = 'Ca edge Energy(eV) Fyield EdgeJump' info_l3 = ' L3 %.1f %.5f %.2f' % xray_edge('Ca', 'L3') info_l2 = ' L2 %.1f %.5f %.2f' % xray_edge('Ca', 'L2') info_l1 = ' L1 %.1f %.5f %.2f' % xray_edge('Ca', 'L1') write_ascii('CaMu.dat', energies, muca_elam, muca_chantler, info_head, info_l3, info_l2, info_l1, label='Energy MuCa_Elam MuCa_Chantler') ######################## I'm not sure that gives a lot of insight except that not trusting Chantler's values for these values might be reasonable. On Thu, Sep 24, 2015 at 10:16 AM, Matthew Marcus wrote:

I'm not after absolute data, just the edge-jump ratio. This would have to be extracted by peak+arctan fitting because any spectra will have peaks and a very limited range between edges. If the Chantler numbers are incorrect, then perhaps the edge-jump ratio is really 2.

Do you have a reference which can be cited?

I'll try the CXRO tool next, since CXRO specializes in soft X-rays. mam

On 9/23/2015 11:49 PM, Jana Padeznik Gomilsek wrote:

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It is very hard to measure or to calculate absolute absorption data, especially in the vicinity of the absorption edges and especially in the soft x-ray region. Therefore there are significant differences between the tables and I think nobody knows which are better. Chantler, for example, says the expected uncertainties of the tables in your region are 50 % to 100 % ( http://physics.nist.gov/PhysRefData/FFast/Text2000/sec06.html#tab2). I would doubt the Chantler's L3+.1 number, all other numbers look ok - this is what you can get.

jana padeznik gomilsek

Message: 3

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Date: Wed, 23 Sep 2015 18:02:08 -0700 From: Matthew Marcus To: XAFS Analysis using Ifeffit Subject: [Ifeffit] Problem with Hephaestus at Ca L-edges Message-ID:<56034B90.70405@lbl.gov> Content-Type: text/plain; charset=utf-8; format=flowed

I wanted to work out the edge-jump ratio between the L3 and L2 edges of Ca using Hephaestus. I ran into two problems:

1. The ratio implied by what it says for the unit-edge-step thickness does not agree with that derived by computing the absorption (cm^2/gm) above and below each edge and dividing the difference (L3+ - L3-)/(L2+ - L2-).

2. The results differ wildly depending on which resource I use:

L3-.1 L3+.1 L2-.1 L2+.1 (L1+ - L1-)/(L2+ - L2-) Elam 4759.796 27837.796 27478.018 38434.277 2.106375908 Chantler 4322.6 6547.121 32827.61 35436.543 0.852655473 Cromer-Leiberman 4288.524 33471.375 32786.294 47072.991 2.042659055

The Henke table doesn't yield an L2 edge jump at all, while the Shaltout yields the same results as Cromer-Leiberman. Which one should I trust and why?

This is old-style H. (V0.18), not Demeter. mam

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--Matt