Any thoughts and opinions would be greatly appreciated as this relates

Dear All It is unfortunate that the questions that were asked by Mark appeared to be phrased is such a way to get the responses that were obtained rather than discussing the real issues behind the questions, or whether they reflected the information in the Review. As such, I feel compelled to reply to these comments as they are not an accurate reflection of what was detailed in my article in Coordination Chemistry Review. While scientific debate is welcome, as are corrections to errors, I believe that is important that these information sites should not be used to give incorrect information as to the contents of a paper. 1. Nowhere in this Coord Chem Rev article did I state that the SS resolution equation does not apply to paths involving MS contributions, so the question was incorrectly phrased, as were the responses that claim the paper was incorrect in saying this. What I did say was that MS analyses can distinguish metal-ligand bond lengths that differ by less than the resolution imposed by this equation if the MS pathways from the different ligands are sufficiently different (within the inherent Fourier transform resolution) to get around this problem. There are numerous examples in the literature where metal-ligand bond lengths that differ by less than the SS resolution have been distinguished in this manner and have been verified by comparing crystal structure information with those obtained from MS analyses. Here is a direct copy of the relevant section from the paper, so I am uncertain as to how the contributors to the e-mails can come to the conclusion that I stated that the equation does not apply to resolution in MS paths. Clearly, I have stated that it is only when this resolution is sufficiently different in other atoms of the restrained ligands that metal-ligand bond lengths that have differences less than the SS resolution of bond lengths can be distinguished (the article only talked about ligands treated as restrained entities). This limit on the resolution of distances arises because the larger the k range, the greater the separation of the individual oscillations at the end of the k range. While this equation is often quoted, the resolution of the peaks in the FT corresponding to different shells improves as the temperature is lowered due to reduction in the Debye-Waller factors, so it should only be taken as a reasonable guide. Thus the use of as large a k range as possible not only improves the determinacy of the problem, but it also improves the precision and accuracy to which individual metal-ligand bond lengths are determined, and whether individual bond lengths can be resolved. With the typical k ranges used in SS XAFS analysis, M-L bond differencs have to differ by 0.1-0.2 Å for the oscillations in the XAFS to be sufficiently resolved to distinguish between these two bond lengths. By contrast, MS analysis of XAFS data has the ability to distinguish between metal-ligand bond distances that differ by a factor that is less than the ~0.1 Å limit imposed by the SS resolution, provided that the groups to which the ligand donor atoms are attached have quite different MS contributions, which is often the case. The differentiation of M-L bond distances that are less than the resolution obtainable with SS analysis relies on the MS contributions of other atoms within the ligands, since these normally have sufficiently different frequencies of oscillations in the XAFS so that they can be resolved. The MS contributions are most important in the low k range [18] and hence, the most accurate and precise bond length determinations in terms of resolution of different shells (and three-dimensional structural determination) will be obtained when both a large k range and all of the low k range data are used in the fitting procedure. What do the above comments mean in practice? It means that if a complex has ligands all of the same type and angles that involve the M-ligand bond and the ligand are essentially the same, then MS analysis cannot improve over SS on separating bond distances that differ by less than the SS resolution in the FT. However, if ligands of the same type are at different angles with respect to the metal-ligand axes or have different ligands adjacent or opposite to them, or if different ligands are at similar distances, then there is almost certainly a range of MS paths that have half distances that differ by more than the resolution given by the equation and, hence, the individual metal-ligand distances can be distinguished by the use of MS fitting within the constraints of the equation that was given, when they cannot be distinguished by SS fitting. 2. With regard to point 2, yes the equation should have been more accurately described as the number of independent observations rather than the number of independent points in reference to equation 24 in the review. The number of independent observations is a combination of the number of independent points in the EXAFS data plus the number of independent observations obtained from crystallography that are included in the restrained model, as described in the Binsted, Strange and Hasnain article. The equation (or variations of it, as pointed out by the comments below) is, however, appropriate for use in estimating the value of the number of independent observations that are included in restrained MS modeling for fits to EXAFS data. This is not only used in such EXAFS analyses but also extensively, and for a long time, in protein crystallography to increase the degree to which a fit is overdetermined or to prevent an underdetermined fit to the data. As pointed out by Matt, this is often used for relatively rigid ligands, such as imidazoles; it can also be used for flexible ligands where the internal bond lengths vary over a narrow range that is defined by X-ray crystallography, but one of more angle(s) have significant flexibility. For the former case, the whole ligand is moved as an essentially rigid entity, in much the same way as a single atom in the fitting procedure. The essentially fixed (within small ranges) bond angles and bond lengths involving this group lead to the extra term in the equation that is the number of independent observations that are included in the model and, in a restrained model, this increases the value of N/p, even though the value of p does not change (i.e., the positional parameters within the imidazole, for instance, are also fitted but within a very narrow range that is consistent with the variation observed in accurate X-ray crystallography structures). If these bond lengths and angles (and/or Debye-Waller values) were constrained, then the value of p would also decrease making the problem more overdetermined. The Debye-Waller factors can be calculated for atoms in a ring in order to reduce the value of p, but extreme care has to be taken in the use of these values in constrained fits, since they take no account of disorder problems in the crystal or solution and, hence, could result in constrained values that are artificially low and which would lead to problems in the fitting procedure. The answer to the question is that the Stern paper discusses the number of independent points in the EXAFS data and applies to both SS and MS fitting. However, for restrained MS fits, the number of independent observations that should be used in assessing the degree to which the problem is determined in the fitting procedure is that described in the Binsted, Strange and Hasnain paper (or something similar). The latter type of fitting was that described in the Coordination Chemistry Rev article and presumably has been used in the work described by Mark. All the best Peter HI Mark, directly to corrections suggested to be made to my PhD thesis! This is going to re-iterate most of what Bruce said, but since you asked:

1)Does the equation for bond distance resolution (r = pi/2deltak) only apply to SS?

No. It applies to all EXAFS.

I have held the opinion that this can be applied to MS analysis

You have been right.

however I have recently been informed that this equation does not correctly describe distance > resolution in MS analyses. The paper in Coord. Chem. Rev. 2005, 249, 141-160 describes this > and is this concordant with the views of the wider EXAFS community?

You were mis-informed. This paper is profoundly wrong, and is not concordant with the views of the wider EXAFS community, as defined by the standards and criteria documents at http://www.i-x-s.org/OLD/subcommittee_reports/sc/err-rep.pdf This paper states that the number of independent points in an XAFS data set is: N_i = [ 2*(rmax - rmin) * (kmax -kmin) / pi ] + Sum D*(N-2) + 1 Here rmin,rmax,kmin, and kmax are the spectral ranges. I cannot tell what the sum is over, but D is the "dimension with a restrained part of the model (ie, three for a three-dimensional model)" and N is "the number of independent atoms within the restrained group of the model". The ( Sum D*(N-2) ) term asserts that the number of independent points in the data is dependent on the model. This is complete nonsense. For what it's worth, the standards and criteria report cited above recommends using N_i = [ 2*(rmax - rmin) * (kmax -kmin) / pi ] rounded to the nearest integer. The report is has a bit more to say, but note that it is carefully (and deliberately) silent on "+1", "+2", etc. This is because N_i is an estimate of the maximum number of parameters that can be extracted from a signal. If you're quibbling whether to add 1 or 2 to this number, it probably means you should really subtract 4. Now, one may apply a variety of modeling approaches (tricks?? assumptions??) to the analysis of multiple scattering in highly constrained three-dimensional models that are often associated with organo-metallics. For example, a histidine ring attached to a metal will give multiple scattering, and you can usually assert that the ring is rigid, though you may need to refine its location and orientation relative to the metal. That makes the bond distances and angles (and MS amplitudes) for all the scattering paths from this ring all dependent on a reduced number of variables. It does not add information to the data. Cheers, --Matt _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit X-Account-Key: account2 X-Mozilla-Keys: Return-Path: X-Original-To: j.aitken@chem.usyd.edu.au Delivered-To: aitken_j@chem.usyd.edu.au Received: from localhost (unknown [127.0.0.1]) by localhost.chem.usyd.edu.au (Postfix) with ESMTP id 3F99881B8; Thu, 7 Jun 2007 07:04:39 +1000 (EST) X-Virus-Scanned: amavisd-new at chem.usyd.edu.au Received: from tismis.chem.usyd.edu.au ([127.0.0.1]) by localhost (tismis.chem.usyd.edu.au [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id FIIBlvbv0FPG; Thu, 7 Jun 2007 07:04:36 +1000 (EST) Received: from millenia.cars.aps.anl.gov (millenia.cars.aps.anl.gov [164.54.160.111]) by tismis.chem.usyd.edu.au (Postfix) with ESMTP id 1AFAB8187; Thu, 7 Jun 2007 07:04:35 +1000 (EST) Received: from millenia.cars.aps.anl.gov (localhost.localdomain [127.0.0.1]) by millenia.cars.aps.anl.gov (8.13.8/8.13.8) with ESMTP id l56L3Xc7017917; Wed, 6 Jun 2007 16:03:34 -0500 Received: from polyhymnia.mr.aps.anl.gov (polyhymnia.mr.aps.anl.gov [164.54.244.23]) by millenia.cars.aps.anl.gov (8.13.8/8.13.8) with ESMTP id l56L3WHx017914 for ; Wed, 6 Jun 2007 16:03:32 -0500 Received: from localhost (localhost [127.0.0.1]) by polyhymnia.mr.aps.anl.gov (8.13.8/8.13.8/Debian-3) with ESMTP id l56L0im6015827; Wed, 6 Jun 2007 16:00:44 -0500 From: Bruce Ravel Organization: Molecular Environmental Science Group at Argonne National Lab To: XAFS Analysis using Ifeffit Date: Wed, 6 Jun 2007 16:00:43 -0500 User-Agent: KMail/1.9.6 References: <200706061213.DGT11246@auummr1om07.three.com.au> In-Reply-To: <200706061213.DGT11246@auummr1om07.three.com.au> MIME-Version: 1.0 Content-Disposition: inline Message-Id: <200706061600.43646.bravel@anl.gov> Cc: MarkBondin Subject: Re: [Ifeffit] bond distance resolution and correlation of parameters in MS analyses? X-BeenThere: ifeffit@millenia.cars.aps.anl.gov X-Mailman-Version: 2.1.9 Precedence: list Reply-To: Bruce Ravel , XAFS Analysis using Ifeffit List-Id: XAFS Analysis using Ifeffit List-Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit, mailto:ifeffit-request@millenia.cars.aps.anl.gov?subject=unsubscribe List-Archive: http://millenia.cars.aps.anl.gov/pipermail/ifeffit List-Post: mailto:ifeffit@millenia.cars.aps.anl.gov List-Help: mailto:ifeffit-request@millenia.cars.aps.anl.gov?subject=help List-Subscribe: http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit, mailto:ifeffit-request@millenia.cars.aps.anl.gov?subject=subscribe Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: ifeffit-bounces@millenia.cars.aps.anl.gov Errors-To: ifeffit-bounces@millenia.cars.aps.anl.gov On Wednesday 06 June 2007, MarkBondin wrote:

2) What is the actual equation which defines the determinacy of a fitting procedure and does this differ between SS and MS analyses? For MS analyses there has been a recently published equation (Coord. Chem. Rev. 2005, 249, 141-160) which takes into acount the number of dimensions used in the analyses and is this only relevant to MS analyses of data? This has also been expressed in the paper by Binsted (Biochemistry. 1992, 31, 12117-12125) however a different equation has been detailed by Stern (Phys. Rev. B. 1993, 48, 9825-9827) which I have been using as a guide in my MS analyses. Is this acceptable?

1. I don't know what you mean by the word "determinacy". In any case, I thought I made it clear in my last post that, in my opinion, the differences between SS and MS analysis are in the physical interpretation and not in the statistical interpretation. Feff, Ifeffit, and Artemis certainly go to great lengths to downplay the differences between SS and MS paths in the context of the formalism of the theory and analysis, instead emphasizing their differences only in the context of physical interpretation. 2. Argonne's library only has access to the last year of Coord. Chem. Rev. and I don't have time this week to go fetch it from the stacks. So I cannot comment on that paper. 3. The paper by Stern should be read with some care. The argument Ed makes in that paper can only be true in the case of a perfectly packed signal. EXAFS data, although treated as signal processing problem, is never perfectly packed. The Nyquist criterion is an upper bound on the information content, but the actual content of the data is always somewhat less. There are some very fine papers by Rossner and Krappe about using Baysian techniques to find the actual information content of the EXAFS signal. The executive summary is that if think you need Ed's magic "+2", you are probably overusing the information content of your data. Most of us here in this list aren't as careful in practice as all that Baysian stuff. In general, one tries to stay "well below" the Nyquist upper bound. If your fitting parameters make sense physically, if the correlations are not "too high", and if the error bars on your parameters are not "too big", then you are probably not overusing the information content of your data. What is "too high" and "too big"? Well, I am purposefully using squishy language. It is kind of difficult to use Gaussian statistical techniques on EXAFS data, despite the fact that that's exactly what Ifeffit does. The reason is that Gaussin statistics presumes that your measurememt errors are statistical and normally distributed. In practice, exafs analysis is dominated by systematic uncertainties. Things like detector or sample non-linearities and the approximations made by Feff are much bigger sources of error than shot noise for most experiments. Most of those systematic problems are present in your analysis, but I have no idea how you could possibly quantify them. Hence I find myself using squishy language to discuss fit statistics. Read the papers by the frequent contributors to this mailing list. Scott Calvin and Shelly Kelly in particular are careful EXAFS practitioners who work on tough analysis problems and deal well with these issues. Doing what they do may not be as right as possible, but it certainly ain't wrong. HTH, B -- Bruce Ravel ---------------------------------------------- bravel@anl.gov Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007 Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793 My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/ _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit Return-Path: X-Original-To: j.aitken@chem.usyd.edu.au Delivered-To: aitken_j@chem.usyd.edu.au Received: from localhost (unknown [127.0.0.1]) by localhost.chem.usyd.edu.au (Postfix) with ESMTP id A3DA68195; Wed, 6 Jun 2007 22:51:48 +1000 (EST) X-Virus-Scanned: amavisd-new at chem.usyd.edu.au Received: from tismis.chem.usyd.edu.au ([127.0.0.1]) by localhost (tismis.chem.usyd.edu.au [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id jldjzjMckVWz; Wed, 6 Jun 2007 22:51:47 +1000 (EST) Received: from millenia.cars.aps.anl.gov (millenia.cars.aps.anl.gov [164.54.160.111]) by tismis.chem.usyd.edu.au (Postfix) with ESMTP id 75D278160; Wed, 6 Jun 2007 22:51:47 +1000 (EST) Received: from millenia.cars.aps.anl.gov (localhost.localdomain [127.0.0.1]) by millenia.cars.aps.anl.gov (8.13.8/8.13.8) with ESMTP id l56CnoPv011737; Wed, 6 Jun 2007 07:49:51 -0500 Received: from polyhymnia.mr.aps.anl.gov (polyhymnia.mr.aps.anl.gov [164.54.244.23]) by millenia.cars.aps.anl.gov (8.13.8/8.13.8) with ESMTP id l56CnmLn011734 for ; Wed, 6 Jun 2007 07:49:48 -0500 Received: from localhost (localhost [127.0.0.1]) by polyhymnia.mr.aps.anl.gov (8.13.8/8.13.8/Debian-3) with ESMTP id l56Cl1cT014080; Wed, 6 Jun 2007 07:47:01 -0500 From: Bruce Ravel Organization: Molecular Environmental Science Group at Argonne National Lab To: ifeffit@millenia.cars.aps.anl.gov Date: Wed, 6 Jun 2007 07:47:01 -0500 User-Agent: KMail/1.9.6 References: <200706061213.DGT11246@auummr1om07.three.com.au> In-Reply-To: <200706061213.DGT11246@auummr1om07.three.com.au> MIME-Version: 1.0 Content-Disposition: inline Message-Id: <200706060747.01272.bravel@anl.gov> Cc: MarkBondin Subject: Re: [Ifeffit] bond distance resolution and correlation of parameters in MS analyses? X-BeenThere: ifeffit@millenia.cars.aps.anl.gov X-Mailman-Version: 2.1.9 Precedence: list Reply-To: Bruce Ravel , XAFS Analysis using Ifeffit List-Id: XAFS Analysis using Ifeffit List-Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit, mailto:ifeffit-request@millenia.cars.aps.anl.gov?subject=unsubscribe List-Archive: http://millenia.cars.aps.anl.gov/pipermail/ifeffit List-Post: mailto:ifeffit@millenia.cars.aps.anl.gov List-Help: mailto:ifeffit-request@millenia.cars.aps.anl.gov?subject=help List-Subscribe: http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit, mailto:ifeffit-request@millenia.cars.aps.anl.gov?subject=subscribe Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 8bit Sender: ifeffit-bounces@millenia.cars.aps.anl.gov Errors-To: ifeffit-bounces@millenia.cars.aps.anl.gov On Wednesday 06 June 2007, MarkBondin wrote:

1)Does the equation for bond distance resolution (r = pi/2deltak) only apply to SS? I have held the opinion that this can be applied to MS analysis however I have recently been informed that this equation does not correctly describe distance resolution in MS analyses. The paper in Coord. Chem. Rev. 2005, 249, 141-160 describes this and is this concordant with the views of the wider EXAFS community?

Mark,

Strictly speaking, that equation doesn't have anything to do with EXAFS. That is the equation that tells you what your Fourier component resolution is in a general Fourier analysis problem. It just so happens that, in the case of single scattering EXAFS analysis, that equation is easily interpreted in terms of photoelectron wavenumber k and SS path length r.

The equation is neither different nor incorrect for MS analysis. That's true becuase MS analysis isn't any different from SS analysis. In either case, you do a Fourier transform. In either case, you attempt to model Fourier components using the contributions from some number of scattering geometries as computed by theory. In either case, you are asking yourself if you can actually resolve small differences in phase of the various things that contribute to the fit.

The only difference lies in how you *interpret* the physical meaning of the Fourier components. And even then, things aren't so very different. In the case of SS analysis, you assert that the R axis is a measure of "bond length" while for MS analysis the R axis is a measure of "half path length" -- acknowledging, of course, that there is a phase shift in the EXAFS equation such that the R axis actually measures something a bit shorter than the bond or half path length.

Off the top of my head, I don't recall the paper you cite and I most certainly cannot speak for the "wider EXAFS community". Speaking for myself, the physical interpretation of the equation for Fourier component resolution may change when you consider MS paths, but to claim that a property of the Fourier transform somehow becomes invalid when you change the details of the fitting model is just silly.

B

-- Bruce Ravel ---------------------------------------------- bravel@anl.gov

Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007

Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793

My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/

_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

Return-Path: X-Original-To: j.aitken@chem.usyd.edu.au Delivered-To: aitken_j@chem.usyd.edu.au Received: from localhost (unknown [127.0.0.1]) by localhost.chem.usyd.edu.au (Postfix) with ESMTP id B52C68192; Wed, 6 Jun 2007 22:34:01 +1000 (EST) X-Virus-Scanned: amavisd-new at chem.usyd.edu.au Received: from tismis.chem.usyd.edu.au ([127.0.0.1]) by localhost (tismis.chem.usyd.edu.au [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Bt1hFrBPzdYS; Wed, 6 Jun 2007 22:34:01 +1000 (EST) Received: from millenia.cars.aps.anl.gov (millenia.cars.aps.anl.gov [164.54.160.111]) by tismis.chem.usyd.edu.au (Postfix) with ESMTP id 8255C8160; Wed, 6 Jun 2007 22:34:00 +1000 (EST) Received: from millenia.cars.aps.anl.gov (localhost.localdomain [127.0.0.1]) by millenia.cars.aps.anl.gov (8.13.8/8.13.8) with ESMTP id l56CVHTh011592; Wed, 6 Jun 2007 07:31:35 -0500 Received: from petasus.aps.anl.gov (petasus.aps.anl.gov [164.54.146.72]) by millenia.cars.aps.anl.gov (8.13.8/8.13.8) with ESMTP id l56CDQCl011430 for ; Wed, 6 Jun 2007 07:13:26 -0500 Received: from herald.aps.anl.gov (herald.aps.anl.gov [164.54.50.61]) by petasus.aps.anl.gov (8.13.7/8.13.7) with ESMTP id l56CDPH7020467 for ; Wed, 6 Jun 2007 07:13:25 -0500 (CDT) Received: from iota.aps.anl.gov (iota.aps.anl.gov [164.54.56.65]) by herald.aps.anl.gov (8.13.7/8.13.7) with ESMTP id l56CDDTr015527 for ; Wed, 6 Jun 2007 07:13:13 -0500 (CDT) Received: from auummr1om07.three.com.au (smtpout3.three.com.au [202.124.68.59]) by iota.aps.anl.gov with ESMTP id l56CDBRl028957 for ; Wed, 6 Jun 2007 07:13:12 -0500 (CDT) Received: from auumgu1pr04.three.com.au (auummr1vp02.three.com.au [10.176.58.185]) by auummr1om07.three.com.au (MOS 3.5.5-GR) with ESMTP id DGT11246; Wed, 6 Jun 2007 22:13:03 +1000 (EST) Message-Id: <200706061213.DGT11246@auummr1om07.three.com.au> Content-Disposition: inline MIME-Version: 1.0 X-Mailer: Perl5 Mail::Internet v1.40 From: MarkBondin To: "ifeffit@millenia.cars.aps.anl.gov" Date: Wed, 06 Jun 2007 22:13:03 +1000 (EST) X-Priority: 3 (Normal) X-MIME-Autoconverted: from quoted-printable to 8bit by millenia.cars.aps.anl.gov id l56CDQCl011430 X-Mailman-Approved-At: Wed, 06 Jun 2007 07:31:16 -0500 Subject: [Ifeffit] bond distance resolution and correlation of parameters in MS analyses? X-BeenThere: ifeffit@millenia.cars.aps.anl.gov X-Mailman-Version: 2.1.9 Precedence: list Reply-To: XAFS Analysis using Ifeffit List-Id: XAFS Analysis using Ifeffit List-Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit,

mailto:ifeffit-request@millenia.cars.aps.anl.gov?subject=unsubscribe List-Archive: http://millenia.cars.aps.anl.gov/pipermail/ifeffit List-Post: mailto:ifeffit@millenia.cars.aps.anl.gov List-Help: mailto:ifeffit-request@millenia.cars.aps.anl.gov?subject=help List-Subscribe: http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit, mailto:ifeffit-request@millenia.cars.aps.anl.gov?subject=subscribe Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 8bit Sender: ifeffit-bounces@millenia.cars.aps.anl.gov Errors-To: ifeffit-bounces@millenia.cars.aps.anl.gov

Hi, I would like general opinions of some EXAFS practioners in regards to the most widely accepted methods for bond distance resolution and correlation of parameters in both single scattering (SS) and multiple scattering (MS) EXAFS refinements and if these can be said to differ?

1)Does the equation for bond distance resolution (r = pi/2deltak) only apply to SS? I have held the opinion that this can be applied to MS analysis however I have recently been informed that this equation does not correctly describe distance resolution in MS analyses. The paper in Coord. Chem. Rev. 2005, 249, 141-160 describes this and is this concordant with the views of the wider EXAFS community?

2) What is the actual equation which defines the determinacy of a fitting procedure and does this differ between SS and MS analyses? For MS analyses there has been a recently published equation (Coord. Chem. Rev. 2005, 249, 141-160) which takes into acount the number of dimensions used in the analyses and is this only relevant to MS analyses of data? This has also been expressed in the paper by Binsted (Biochemistry. 1992, 31, 12117-12125) however a different equation has been detailed by Stern (Phys. Rev. B. 1993, 48, 9825-9827) which I have been using as a guide in my MS analyses. Is this acceptable?

Any thoughts and opinions would be greatly appreciated as this relates directly to corrections suggested to be made to my PhD thesis!

Many thanks,

Mark

_

Professor Peter A. Lay FAA ARC Australian Professorial Fellow and Personal Chair in Inorganic Chemistry Centre for Heavy Metals Research School of Chemistry The University of Sydney NSW 2006 Australia Tel: +61-2-9351 4269 Fax: +61-2-9351 3329