It sounds like a good idea but you will still need to know whether the best fit results for the bond length and third cumulant are correct. Since they are expected to vary widely for different cluster sizes and different substrates and different atmospheres, you should first try to see if your method will work for a more simple system where you know what the bond length and third cumulant should be, i.e. bulk Pt.
Besides, you may find something similar to what you are proposing in Bus and v.Bokhoven's article.

Anatoly

Sent from my mobile phone, please forgive typos

From: JeongEunSuk <eunsuk1986@hotmail.com>
To: ifeffit <ifeffit@millenia.cars.aps.anl.gov>
Sent: Mon, May 7, 2012 04:02:06 GMT+00:00
Subject: [Ifeffit] (no subject)

Hello
I measured temperature-dependent EXAFS at Pt L3 edge with Pt nanoparticles in room and high temperature(400 C). I have some questions about thermal vibration in EXAFS fit. I read that third and fourth culmulants related with phase and amplitude in anharmonic term, respectively. especially, I concerned third culmulant to relate with phase.
As you know, the phase also relates with bonding length. So that, the bonding length between Pt-Pt pair considerably correlated with third culmulant. So I can't decide exact bonding length and third culmulant because their correlation. I think that the relation of both bonding length and third culmulant is similar to that of number and debye-waller factor.
Is it right to find bonding length and third culmulant like finding number and debye-waller factor using k-weight?