# Rotational oscillator?
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## Non-rigid rotor
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https://sci.tanta.edu.eg/files/Microwave%20spectroscopy%20BSc-Lect-2.pdf
irregular not-equidistant levels
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## Tunneling - https://en.wikipedia.org/wiki/Pyramidal_inversion
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[Ammonia - more is different](http://www.tcm.phy.cam.ac.uk/~bds10/aqp/anderson72more_is_different.pdf)
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# Parents
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* TLS - pseudospin or spin of $SU(2)$?⏎