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Where would I find what a gas breaks down into when it....

  1. Sep 28, 2015 #1
    ... becomes a plasma?

    I am trying to find information on the species that will be present when a gas is broken down into a plasma for different types of gas and temperatures, is there a list somewhere, please could someone give me an idea of where I should look for this information?

    Also am I correct in assuming that at lower temperatures there is disassociation and higher temperatures there is ionisation? And therefore there would be more radical species at lower temperatures and more chemical reactions in a reactive environment.

    Thanks for any help on this, the plasma physics field is huge and having trouble figuring out where I would locate this information.
  2. jcsd
  3. Sep 28, 2015 #2


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    There are tables of ionization energies, JANAF, ICT, CRC.
  4. Sep 28, 2015 #3
    That's really helpful and thanks for confirming the general case!

    What I really need are, for example for methane:


    Those reactions. Would there be a place where they are grouped or would I have to look up each gas individually?

    Also the differences in products at different temperature i.e. at what temperature there would be ions instead of radicals (like the above) for different gases.
  5. Sep 28, 2015 #4


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    Welcome to the wonderful world of chemical thermodynamics. For the example you've picked, CH4, no one knows, nor has anyone measured, nor is anyone likely to ever be able to measure, or calculate, the distribution of hydrocarbon species in equilibrium for a system having a stoichiometry identical to that for methane (xC = 0.2, xH = 0.8). At ordinary conditions, methane is stable, and can be treated as a single component; at elevated T, P, or in the presence of catalysts, it is necessary to consider either the species population distributions of a two-component system, or a system of an unknown number of components and an unknown number of reactions among those components, the overall system composition still being equivalent to that of pure methane.
    The equilibrium species distributions are of course going to be functions of T, P, {Xi}.
  6. Sep 29, 2015 #5
    ha thanks for the information. hmm this presents a problem, I am trying to compare plasma processes that disassociate different gases to radicals and sonolysis (the use of ultrasound cavitation) to do the same. Clearly the radicals from the water would be H⋅ and OH⋅, but then if I dont know what species will be given from the gas in the water how do I know how they will recombine? The best I can find is this:


    Where I think M would be the species of the dissolves gas.

    But anyway thanks again for your help!

    edit so there is no table type information for temperature of when disassociation for a gas becomes ionisation?
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