HI Mark,
Any thoughts and opinions would be greatly appreciated as this relates 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