I know that molecules can spin around a central axis, but lately I keep wondering if it is possible for a single atom to spin around its own axis (like earth for example). Also does this concept of the orientation of a single atom actually exists?
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2We have to break the symmetry of both, the atom and the external fields to see the quantum mechanical equivalents of "orientation". So we need at least an external electrical or magnetic field in addition to an atom that is not in a radially symmetric s-state. Once we do we can see splitting of spectral lines. How they split tells us about the symmetry of the system. – FlatterMann Jan 20 '24 at 13:47
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This might help. But then again, it might not - How does an isolated electron in deep space 'know' it is spinning? – mmesser314 Jan 20 '24 at 15:15
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I suspect it depends on your definitions. The problem is an atom is not a rigid body. It has a nucleus and electrons, and there is relative movement of electrons with respect to nucleus. So the electrons can have orbital moment, so there can be rotational movement of electrons. So, for example, if we have in mind something like the Bohr model of atom, where electrons rotate around the nucleus, would you say the atom is rotating around its axis? One could have doubts about that, as the electron rotates, but does the nucleus rotate?. However, somebody could say that, strictly speaking, the electrons and the nucleus rotate around their common center of mass, and, experimentally, this is reflected in the spectra of atoms. In general, though, electrons and the nucleus are not connected together rigidly. I would say, for example, a hydrogen atom in a state with orbital momentum does rotate around its axis passing through its center of mass. Let me also note that nuclei can also be excited rotationally.
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