Effects of hydrogen anions in the solar atmosphere

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Discussion Overview

The discussion revolves around the population density, stability, and formation of hydrogen anions (##H^-##) in the solar atmosphere. Participants explore their role in radiative transfer and the implications for opacity in stellar atmospheres, particularly in relation to the Sun.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the population density of ##H^-## anions in the Sun's atmosphere and their stability, suggesting that heat would likely ionize them to protons.
  • Another participant expresses skepticism about the existence of ##H^-## anions, initially believing they would not exist at all, but acknowledges their presence as a significant source of opacity in stellar atmospheres.
  • A later reply elaborates on the formation of ##H^-## anions, explaining that they are created when a hydrogen atom accepts a free electron, which is bound less strongly than the original electron, and that this process releases a photon.
  • Participants discuss the process of photodissociation, where the second electron is stripped from the anion by a higher energy photon, contributing to the opacity in the atmosphere.
  • One participant seeks to quantify the number of ##H^-## anions relative to neutral hydrogen atoms in the Sun's atmosphere but finds no available data.
  • Another participant expresses frustration over the lack of information found through a Google search regarding the topic.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the population density and stability of ##H^-## anions, with no consensus on their abundance or the specific mechanisms limiting their numbers.

Contextual Notes

The discussion highlights limitations in available data on the density of ##H^-## anions and their relationship to neutral hydrogen, as well as the dependence on definitions related to the formation and stability of these anions.

Who May Find This Useful

Readers interested in astrophysics, particularly those studying stellar atmospheres, radiative transfer, and the behavior of ions in high-energy environments may find this discussion relevant.

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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"?
 
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My guess - very rare. Heat would ionize to protons.
 
mathman said:
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?
 
Sorry - google search didn't turn up anything.
 
@mathman - yes, it's frustrating. Thanks for trying though :)
 

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