Can Free Particles in Plasmas Have a Continuous Absorption Spectrum?

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SUMMARY

The discussion centers on the absorption spectrum of free particles in plasmas, specifically addressing whether free electrons can exhibit a continuous absorption spectrum. Participants clarify that while free electrons cannot absorb photons due to conservation laws, they can scatter light through Thomson scattering. The conversation also touches on the Born-Oppenheimer approximation, which allows for the separation of electronic and nuclear movements in molecules, emphasizing that molecular absorption involves quantized energy levels due to rotational and vibrational modes. Ultimately, the consensus is that free particles like electrons do not have a quantized absorption spectrum, while molecules do due to their complex structure.

PREREQUISITES
  • Understanding of Thomson scattering and its role in plasma diagnostics.
  • Familiarity with the Born-Oppenheimer approximation in molecular spectroscopy.
  • Knowledge of energy conservation principles in photon-electron interactions.
  • Basic concepts of molecular rotational and vibrational energy levels.
NEXT STEPS
  • Research the principles of Thomson scattering and its applications in plasma physics.
  • Study the Born-Oppenheimer approximation and its implications for molecular spectroscopy.
  • Explore energy and momentum conservation laws in photon interactions with particles.
  • Investigate the quantization of energy levels in diatomic and polyatomic molecules.
USEFUL FOR

Physicists, chemists, and students interested in plasma physics, molecular spectroscopy, and the interactions of light with matter.

  • #31
(Posted by Dickfore:)
So, how are they free if they are in the vicinity of atoms?
Claude Bile said:
Free as in not bound to a nucleus. Conduction band electrons in a condensed dielectric for example.
The difference between the photoelectric effect, in which the photon's total energy is absorbed by the electron, and Thomson scattering on free electrons, is that a little recoil momentum is absorbed by the recoiling atom or atomic lattice. Conduction electrons are not free electrons; the work function to remove a conduction electron is >= 3 eV.

Bob S
 

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