Editing Particle in a ring (section)

== Application ==

In [[organic chemistry]], [[aromatic]] compounds contain atomic rings, such as [[benzene]] rings (the [[Friedrich August Kekulé von Stradonitz|Kekulé]] structure) consisting  of five or six, usually [[carbon]], atoms. So does the surface of "[[buckyball]]s" (buckminsterfullerene). This ring behaves like a circular [[waveguide]], with the valence electrons orbiting in both directions. To fill all energy levels up to n requires <math>2\times(2n+1)=4n+2</math> electrons, as electrons have additionally two possible orientations of their spins. This gives exceptional stability ("aromatic"), and is known as the [[Hückel's rule]].

Further in rotational spectroscopy this model may be used as an approximation of rotational energy levels.