Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why does Photoionization cross section reduce with frequency?

  1. Sep 27, 2011 #1
    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
  2. jcsd
  3. Sep 27, 2011 #2


    User Avatar
    Science Advisor

    I vaguely recall that it is a resonance effect.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook