Can Free Particles in Plasmas Have a Continuous Absorption Spectrum?

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The discussion centers on whether free particles in plasmas can exhibit a continuous absorption spectrum due to their non-quantized energy states. Participants clarify that while free electrons can absorb energy, they do not do so through traditional absorption but rather through scattering processes like Thomson scattering, which conserves energy and momentum. The conversation also highlights that molecules, unlike free electrons, have quantized energy levels due to their rotational and vibrational degrees of freedom, which contribute to their absorption spectra. The role of translational energy in absorption is debated, with the conclusion that non-resonant light does not significantly increase translational energy in a gas. Ultimately, the complexities of photon interactions with free particles and the implications for spectroscopy are emphasized.
  • #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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