Matt is saying that N and S02 are always 100% correlated for a single path. But in some situations you might know N for one path but not others. For example, you might know that the absorbing atom is octahedrally coordinated to oxygen but not be as certain as to next-nearest neighbors, or that there are copper atoms on the corners of a simple cubic lattice with a mixture of atoms at other positions. In cases like that, both N for all paths but one and S02 can be fit without 100% correlation.

The degeneracy of multiple-scattering paths can often be constrained in terms of the coordination numbers for direct-scattering paths, which can further reduce (not “break”) the correlation.

In terms of the main question, I agree with Matt: I don’t think there’s much point in using the line-crossing technique nowadays; fitting using multiple k-weights simultaneously accomplishes the same thing but is a bit easier to interpret statistically.

—Scott Calvin

Sarah Lawrence College