> On Mar 11, 2015, at 11:13 AM, Keller, Jacob <[log in to unmask]> wrote:
>
> Somebody sent me a pdf with such a mind-picture which describes the origin of the anomalous effect as arising from broken centrosymmetry of the anomalous atoms themselves:
>
> (p. 8) "Under normal conditions, electron distributions within atoms are centrosymmetric...Under conditions of anomalous scattering, electrons are perturbed from their centrosymmetric distributions; electrons are jumping between orbitals. The breakdown of centrosymmetry in the scattering atoms is reflected in a loss of centrosymmetry in the pattern of scattered X-ray intensities."
I think this is wrong. Unless I am mistaken, the diffraction pattern is centrosymmetric simply as a consequence of the electron density (and therefore the potential) being a purely real function. If the function is complex (i.e., including that small perturbation I spoke of this morning), then the diffraction pattern will no longer be centrosymmetric.
|