This is in response to Shelly's post for MS references.  For linear multiple scattering, I like to use this paper:

    Hudson, EA; et. al. (1996) Phys Rev B 54(1) 156-165

It uses the uranyl ion specifically in this example and has a short section in the introduction about the relations between single and multiple scattering D-W parameters.

Hope this is vaguely what you were looking for....

    Sam

Hi Sam and John, I just wanted to say thank-you to the ifeffit mailing list. Sam, the reference was indeed helpful. And thanks to John for his derivation. This is what I learned about relating sigma2 values for the uranyl. For a linear uranyl moiety (UO2), where the atoms are all in a line O1-U-O2, the sigma2 values can be approximated like this: U-O1-U: sigma2-s.s. (single scattering sigma2) U-O1-U-O1-U: sigma2 = 4 * sigma2-s.s. U-O1-U-O2-U: sigma2 ~ 2 * sigma2-s.s. U-O1-O2-U: sigma2 ~ 2 * sigma2-s.s. This information has been published in Hudson et al. PRB V54 n1, pg 156 (1996). Shelly