Now you are in the subtree of Physics public knowledge tree.

Rotational oscillator?

Created over 3 years ago, updated 14 days ago

Non-rigid rotor

https://sci.tanta.edu.eg/files/Microwave%20spectroscopy%20BSc-Lect-2.pdf
irregular not-equidistant levels

Tunneling - https://en.wikipedia.org/wiki/Pyramidal_inversion

Ammonia - more is different