How does a system consisting of two nuclei have rotational symmetry?

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Discussion Overview

The discussion revolves around the concept of rotational symmetry in a system consisting of two nuclei, particularly in the context of diatomic molecules. Participants explore the implications of rotational symmetry on the energy levels of electrons and the conditions under which such symmetry is defined.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question the definition of rotational symmetry, noting that everything appears the same after a 360° rotation, which they find uninformative.
  • Others reference the concept of "n-fold rotational symmetry" as a potentially relevant section in the Wikipedia article.
  • One participant argues that if the nuclei are distinct, only a 360° rotation leaves the system unchanged, while a 180° rotation would apply if the nuclei were identical.
  • Another participant seeks clarification on whether the invariance under 360° rotation is sufficient to claim rotational symmetry and its implications for electron energy levels being dependent solely on the distance between the nuclei.
  • It is noted that the rotational symmetry discussed pertains specifically to the central axis, which is the line connecting the two nuclei.

Areas of Agreement / Disagreement

Participants express differing views on the nature of rotational symmetry in the context of distinct versus identical nuclei, and whether the definition provided is adequate to support claims about electron energy levels. The discussion remains unresolved regarding the implications of rotational symmetry.

Contextual Notes

Participants highlight the need for clarity on the definitions and conditions under which rotational symmetry is applied, particularly in relation to the distinctness of the nuclei and the specific rotational angles considered.

AxiomOfChoice
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I don't see it. Can someone explain? The Wikipedia article (http://en.wikipedia.org/wiki/Rotational_symmetry) defines an object with rotational symmetry as an object that looks the same after a certain amount of rotation. But this seems vacuous; doesn't *everything* look the same after a 360[itex]^\circ[/itex] rotation?
 
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Keep reading; especially the section titled "n-fold rotational symmetry".
 
Doc Al said:
Keep reading; especially the section titled "n-fold rotational symmetry".
I still don't see it. If the nuclei are distinct (say, oxygen and hydrogen), and they are initially at (0,1) and (0,-1), respectively, then only rotation through 360[itex]^\circ[/itex] will leave the system unchanged. If the nuclei are not distinct, however, then I see how rotation through 180[itex]^\circ[/itex] will leave the system unchanged. But I'm not assuming that the nuclei are identical.
 
OK, then I don't get your point. Where does it claim that such a system has anything other than trivial rotational symmetry (except about its central axis, of course)?
 
Doc Al said:
OK, then I don't get your point. Where does it claim that such a system has anything other than trivial rotational symmetry (except about its central axis, of course)?
Sorry; maybe I should be more specific. I'm reading a paper, and the argument is made that, because of the "rotational symmetry" of a diatomic molecule, the energy levels of the electrons depend only on the magnitude of the distance between the two nuclei. Does the fact that the system is invariant under 360-degree rotation mean it has rotational symmetry? If so, why should that be sufficient for us to conclude that the electron energy levels are only dependent on the distance between the nuclei and not their orientation?
 
AxiomOfChoice said:
I'm reading a paper, and the argument is made that, because of the "rotational symmetry" of a diatomic molecule, the energy levels of the electrons depend only on the magnitude of the distance between the two nuclei.
The rotational symmetry referred to is with respect to the central axis (the line between the two nuclei).
 

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