> Something for you to chew on: how is it that the electrons of the protein,
> which are presumably not in phase with each other nor in exactly the same
> place in their orbitals from unit cell to unit cell (maybe they are?) when
> they scatter the photons, they result in interference? What are the chances
> that the scattering electrons are exactly in the same place as the
> electrons in another unit cell, or of the same phase? And would they not
> need to be in the same place to sub-angstrom precision to scatter
> coherently?
They do not need to be in the same place to sub-angstrom precision.
The situation is easier to understand when you think about a crystal composed
of small molecules or even better - atoms (e.g. a Silicon crystal).
If all electrons (pointlike particles) were in the same place, atomic
scattering factor would be a flat function against the scattering angle (the
atomic scattering factor would be a constant function (putting aside
polarization considerations)) and we would not observe a falloff of
intensities for large scattering angles.
By the way, thinking in terms of orbitals can be a bit misleading, because
orbitals are like components of a vector: in different coordinate systems one
gets different sets of components. What has a physical meaning is a wave
function. The wave function can be decomposed into orbitals (localized,
delocalized etc.) in many different ways.
Andrzej
______________________
Andrzej Olczak
Institute of General and Ecological Chemistry
Technical University of Lodz
Zeromskiego 116
90-924 Lodz
Poland
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