Why does Photoionization cross section reduce with frequency?

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SUMMARY

The discussion centers on the phenomenon of photoionization, specifically regarding the reduction of the ionization cross section with increasing frequency. The user seeks clarification on why, after surpassing a certain energy threshold, the rate of ionization decreases. It is established that this reduction is linked to resonance effects in the interaction between photons and atoms, particularly in Hydrogen and Helium IGM clouds. Understanding these principles is crucial for astrophysical projects involving ionization processes.

PREREQUISITES
  • Basic understanding of the photoelectric effect
  • Knowledge of ionization processes in astrophysics
  • Familiarity with Hydrogen and Helium atomic structures
  • Concept of resonance in quantum mechanics
NEXT STEPS
  • Research the resonance effects in photoionization
  • Study the ionization cross section in Hydrogen and Helium
  • Explore the relationship between photon energy and ionization rates
  • Investigate the role of frequency in astrophysical heating processes
USEFUL FOR

Astronomy researchers, astrophysicists, and students studying photoionization and its effects on cosmic structures, particularly those focusing on Hydrogen and Helium IGM clouds.

bushnoh
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I'm currently starting a large comp-astro project, and trying to understand a bit of the background about heading of Hydrogen and Helium IGM clouds I am a bit confused about the the actual heating process.

From the standard photoelectric effect, frequency has to pass a certain frequency (or energy) threshold for ionization to occur but beyond this threshold why does the ionization cross section reduce (rate of ionization)?

I've scoured the internet for several days and not come up with any answers...

Please help, thanks :D
 
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I vaguely recall that it is a resonance effect.
 

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