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Is 3s to 2s transition for Hygrogen forbidden?

  1. Jul 16, 2009 #1
    For hydrogen emission spectra from n = 3 to n = 2:

    My question is: In the following transition which is (are) possible or impossible and why?

    3s --> 2s, 3s --> 2p
    3p --> 2s, 3p --> 2p,
    3d --> 2s, 3d --> 2p,
  2. jcsd
  3. Jul 17, 2009 #2
    Selection rules! If you have a copy of Griffiths' "Introduction to Quantum Mechanics", take a look at section 9.3.3.
  4. Jul 17, 2009 #3


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    You need to have [tex]\Delta l = \pm 1[/tex] for any transition.
  5. Jul 17, 2009 #4
    The number of observed hydrogen spectrum lines is much fewer than theoretically expected.

    Atomic physics by Max Born
    In page 167, it is written as follows,

    The case of hydrogen is peculiar in one respect. Experiment gives distinctly fewer terms than are specified in the term scheme of fig 9; for n=2 only two terms are found, for n=3 only three, and so on.
    The theoretical calculation shows that here (by a mathematical coincidense, so to speak) two terms sometimes coincide, the reason beeing that the relativity and spin corrections partly compensate each other.

    It is found that terms with the same inner quantum number j but different azimuthal quantum numbers l always strictly coincide.

    Hydrogen atom has only one electron. So is it relevant?

    To search spectrum line, please see http://physics.nist.gov/PhysRefData/ASD/lines_form.html
    and enter "H" into "Spectrum" part. "Observed wavelength" is observed line, and "Configurations" is theoretically permitted transition.

    Even if we consider selection rules(due to spin 1 of photon), the observed spectrum lines are fewer than expected.
    Last edited: Jul 17, 2009
  6. Jul 17, 2009 #5
    It is valid for one-photon transition. For many-photon transitions this is not true. Such processes occur, just with much smaller probability.
  7. Jul 17, 2009 #6


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    Thank you for the correction :)
  8. Jul 17, 2009 #7


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  9. Jul 20, 2009 #8
    The selection rules are not "broken" so much as supplemented when you introduce the corrections. For example, when you introduce fine and hyperfine structure corrections, you get more selection rules.

    One thing to note about selection rules, what you are calling "selection rules" are "selection rules for a electric dipole transition", you can have higher order electric transitions and you can have magnetic transitions, which will follow different rules. Magnetic dipole, quadrupole, etc and electric quadrupole, etc transitions are orders of magnitude less likely to occur, and so are often ignored. So cases where you see them broken, they may just not be electric dipole transitions.
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