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Does a Buckyball spin like an electron or like a baseball?

  1. Aug 27, 2015 #1

    jimgraber

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    Does a Buckyball spin like an electron or like a baseball?

    We are often told that an electron does not really spin like a baseball.

    Only one (or two, if you count up and down) spin states, for example.

    How about a Buckyball?

    Does it spin more like an electron, or more like a baseball?

    Where is the dividing line?

    How can you measure the difference?

    TIA,

    Jim Graber
     
  2. jcsd
  3. Aug 27, 2015 #2

    Bystander

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    What are the angular moments of inertia of "buckeyballs," adamantane, SF6, Xe, and an electron?
     
  4. Aug 27, 2015 #3
    Quantum spin isn't the same thing as spin the way a baseball turns. Elementary particles, hadrons, and nuclei have quantum spin, which is an intrinsic characteristic of it, but doesn't actually represent spinning motion (an electron doesn't even contain 1 spin, it's 1/2 spin.) An electron doesn't spin like a top, it just has spin.

    A bucky ball can spin in space like a top, ergo, it's classical angular momentum.

    As far as I know, there can't be a dividing line because these are two different things?
     
  5. Aug 27, 2015 #4

    jimgraber

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    I read your reply to suggest that all but electrons spin like baseballs. Is this what you intended?
    If so, the dividing line is smaller than I expected. What about a proton or a neutron? Do they also spin like baseballs?
     
  6. Aug 27, 2015 #5

    Bystander

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    Nerp.
     
  7. Aug 27, 2015 #6

    jimgraber

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    I googled around a bit and found this nice write up on why a classical spin model for an electron does not work:
    http://www.physicspages.com/2013/01/16/electron-as-a-classical-spinning-sphere/
    I did not find any useful angular moment of inertia for molecules. Wolfram alpha kept giving me the moment of inertia at a distance of one meter.
    I still do not have any reputable reference that would help answer my questions.
     
  8. Aug 27, 2015 #7

    jimgraber

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    I wonder how it would be to try spinning a molecule like tri-substituted methane with one Florine, one Chlorine and one Bromine, ie HCFClBr.At least in theory you could tell what direction it was pointing.
     
  9. Aug 27, 2015 #8

    jimgraber

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    This nice reference on rotational spectroscopy

    http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/rotrig.html

    seems to discuss a diatomic molecule rotating almost like a baseball, except that the rotation is quantized in discrete steps.

    So does a diatomic molecule rotate more like an electron or more like a baseball?

    I think the answer is more like a baseball.


    I guess you can always say the rotation of the baseball is also quantized into discrete steps, just very small ones
     
  10. Aug 27, 2015 #9

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    Bond lengths of molecules (inter-nuclear distances) are O(0.1 nm). Moments are O(10-47) (H2) to O(10-40(?)) kgm2.
     
  11. Aug 27, 2015 #10

    mfb

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    A buckyball might have intrinsic spin (the purely QM property) - not sure how all the electrons add up. Even if it has, it is small.
    It can certainly rotate (the thing with classical equivalent) - the rotation will still be quantized but a classical rotation is probably not a bad model for such a large molecule.
     
  12. Aug 28, 2015 #11
    I have never understood this myself. The point is often made that quantum spin is different than classical spin. But quantum spin is still quantized angular momentum. These things are not totally unrelated.

    Maybe a different way to ask the question. What happens if a black hole eats a lot of polarized light? To conserve angular momentum something has to give. Does the black hole spin faster or does it have some kind of large quantum spin number attached to it?
     
  13. Aug 28, 2015 #12

    mfb

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    The black hole will spin faster.

    Intrinsic particle spin and orbital motion differ in their g-factor. For orbital motion it is always 1, for particle spins it is not.
     
  14. Aug 28, 2015 #13
    Great, now if I can wrap my head around what this g-factor is I may learn something.
     
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