A look at the term scheme might help to understand the absorption edge
structure - pp 286 and Figure 6-30 BMC.
Best, BR
-----Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of
Keller, Jacob
Sent: Wednesday, March 11, 2015 9:58 AM
To: [log in to unmask]
Subject: [ccp4bb] Basic Anomalous Scattering Theory
Dear Crystallographers,
I have had only a vague understanding of what specific things are happening
with shell electrons at anomalous edges. Specifically, for example, to what
energy of electron-transition does the x-ray k-edge correspond in terms of
orbitals, and is that transition energy actually equal to the energy of the
photon, suggesting that the photon is absorbed (or disappears?) in elevating
the electron? I don't think we say it is absorbed, so how does the energy
come back out, from the electron's falling back down, right? So then there's
a new photon created, or the same one comes back out? Where was it?
Further, I also have heard that the emerging anomalous/resonance photons are
of the same wavelength as the incident radiation, but usually there is
something lost in transitions (even non-fluorescence ones) I thought? Has it
ever been definitively shown that the anomalous photons are of the same
energy as the incident radiation?
In the case of L-edges, why are there three separate edges? Further, if the
resonance occurs when the energies are equal, why does resonance occur at
energies greater than the edge? I don't think this happens in other
resonance phenomena, or does it? If projects a middle-C-tone into a piano,
do all of the lower notes resonate as well, according to the Kramers-Kronig
relation? I think it may actually happen in the mammalian cochlea's
travelling wave, but is it completely general to resonance phenomena?
Just interested, and have wondered these things for a long time in the
background of my mind...
Jacob Keller
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Jacob Pearson Keller, PhD
Looger Lab/HHMI Janelia Research Campus
19700 Helix Dr, Ashburn, VA 20147
email: [log in to unmask]
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