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Simple rate question

  1. Sep 26, 2011 #1
    if i have oxygen + photons => products

    if this is an elementary process, is this a uni-molecular process or a bi-molecular process?

    i.e do we count photons as a molecule?

  2. jcsd
  3. Sep 26, 2011 #2


    User Avatar

    Staff: Mentor

    We don't.
  4. Sep 27, 2011 #3
  5. Oct 8, 2011 #4
    It is bi-molecular because without photons there is not reaction

    Photons are treated as any other reactant. The rate for your process is

    V = k [ oxigen ] [ photons ]

    Under certain conditions this second order looks as pseudo-first order or as pseudo-zero-order.

    For example if photons are in excess then its concentration is approximately constant and the rate can be approximated by the pseudo-first-order

    V = k' [ oxigen ]

    with k' = k [ photons ]

    See http://pubs.acs.org/doi/pdf/10.1021/ed082p37.3 and references therein for a more detailed discussion and examples.
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