Effects of hydrogen anions in the solar atmosphere

[sciFax]

TL;DR

I have some questions concerning $H^-$ hydrogen anions in the Sun's atmosphere.

What is the population density of $H^-$ hydrogen anions in the Sun's atmosphere, how stable are they, what limits their numbers, and since they are the dominant source of opacity in radiative transfer in stellar atmospheres, what do they effectively "hide"?

 

[mathman]

My guess - very rare. Heat would ionize to protons.

 

[sciFax]

My guess - very rare. Heat would ionize to protons.

Before I heard about the $H^-$ anion (a hydrogen atom with TWO electrons), I would have guessed they would not even exist. Apparently they do in fact exist in the solar atmosphere, and in sufficient numbers/abundance that they are "the dominant bound-free opacity source at visible and near-infrared wavelengths in the atmospheres of stars like the Sun and cooler ".

Having done a little more reading on the subject, it would appear the these anions are formed by the acceptance of a free electron, which becomes bound to the H atom, but not so strongly as the original electron in the atom. This is accompanied by the release of a photon. The process of stripping the second electron is known as photodissociation, since that electron is knocked out the anion by another, higher energy photon (and since this leads to a neutral H atom, it's not termed ionization). So this is where the opacity comes from, since a wide range of photon energies can lead to this photodissociation.

So, my one remaining question is: how many of these $H^-$ anions exist in the Sun's atmosphere at anyone time as a proportion to, say, neutral hydrogen atoms?

 

[mathman]

Sorry - google search didn't turn up anything.

 

[sciFax]

@mathman - yes, it's frustrating. Thanks for trying though :)