why accelerated electrons "scatter" light? From Yale's chemistry open class, the professor said when a light passes by an electron, it "pulls" the electron up and down, and emit radiation in all direction. How does this happen? And another question is about the X-ray diffraction. From the picture the textbook shows, when X-ray hits an atom, it's reflected, and because X rays hit lost of different layers , it's reflected separately. It's all about reflection, why we call that x-ray diffraction?


simply put : Scattering is a reflection with change of frequency. From debrogli, Frequency relates to Energy.

Every time the photon collides with an electron, some energy is given to it. How much is determined by quantum mechanics, exactly that much that is necessary to lift the electron to a higher energy state. anything inbetween the original energy and target state does not take place, that discreetness is one of the things that quantum world takes as an axiom.

For this , the energy of the photon is now changed. Thus it's frequency changes.

Now if you have a crystal, where the atoms form a lattice, then you have multiple returning rays, these rays interact like waves falling on each other. you get diffraction.

if you want you can calculate the amounts of each.

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  • $\begingroup$ What's the definition of diffraction? Isn't it "the apparent bending of waves around small obstacles and the spreading out of waves past small openings. " $\endgroup$ – user40003 Feb 20 '14 at 2:06
  • $\begingroup$ yes, when ever you have obstacles, they reflect part and transmit part of the wave. These parts of waves behave as if they were emmited by the obstacle itslef, i.e. they "forget" their orginal source (Huygens theory). But the point is, the observable diffraction can only be observed, when the secondary waves (after the so called bending) interact with some other things. Crystallography, it is the interaction with other waves. $\endgroup$ – Sean Feb 20 '14 at 12:36

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