Yes and a very important one - see Ed Stern's talk at the 2001 EXAFS workshop "advanced methods and tricks etc. " His talk is online. Anatoly -----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov To: ifeffit@millenia.cars.aps.anl.gov Sent: Tue Nov 27 04:44:48 2007 Subject: [Ifeffit] Exafs distance resolution Dear all, Is there a physical limitation determining exafs bond distance resolution? Very often the equation r = pi / 2 deltak is quoted as a measure for bond distance resolution. But as i understand this equation is related to the fourier transform traditionally used for exafs analysis. If exafs fitting is done in k-space, on the raw exafs data without applying fourier or any other filtering transformation is there a physical limitation determining exafs bond distance resolution? This question comes down to the following practical problem. If one has a theoretical model developed using computational chemistry that predicts two different bond lengths within one shell, e.g. an octahedral metal center surrounded by 6 oxygen atoms and this shell is predicted to be split in three subshells for wich the bond length differs only 0.05 angstroms; and this model can be fit very well in k-space with the splitted shell, off course keeping the number of fit parameters below the nyquist criterion. Is there in such a case any physical reason not to fit the experimental data with the splitted shell , but with an averaged 6-atom shell with a larger Debye Waller factor? Best regards, Eric Breynaert _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit