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Finding the ratios of diatomic, monatomic and ionized hydrogen

  1. Feb 7, 2013 #1

    Would a clump of gas in space have some diatomic molecules in it as well? If it does, how do we find the ratio?

    I know that hydrogen gas at room temperature on earth is diatomic. So I guess the state of the gas molecules change like this.

    Diatomic molecules -> Monatomic ground state -> Monatomic first excited -> ... so on until ionization.

    Or do diatomic states have their own excited states as electrons go on to higher and higher energy levels?

    I know that in a gas in thermal equilibrium, the ratio of two populations is given by Boltzmann distribution: [itex]\frac{n_j}{n_i} = \frac{g_j}{g_i} e^{-[(E_j-E_i)/kT]}[/itex]
    I also know that I can use this equation to find the ratios of monatomic hydrogen in different excited states. For example, the ratio of hydrogen in ground state to the first excited state.
    Can I use it to find the ratio of diatomic ground state molecules to monatomic ground state molecules as well? I guess all I have to do is just put in the corresponding energy values?

    Please write down your thoughts.

    Thank you.
    Last edited: Feb 7, 2013
  2. jcsd
  3. Feb 8, 2013 #2


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    Science Advisor

    No, you also have to consider the fact that ionization and dissociation increases the entropy of the system because there are more particles. The Saha equation gives the ratio between ionization levels of some element, or the level of dissociation of a molecule (which is a very similar problem).

    If you search for "saha equation molecular hydrogen" you will find a bunch of answers.
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