Editing Rotational transition (section)

{{Short description|Abrupt change in a quantum particle's angular momentum}}

In [[quantum mechanics]], a '''rotational transition''' is an abrupt change in [[angular momentum]].  Like all other properties of a quantum [[Elementary particle|particle]], [[angular momentum quantization|angular momentum is quantized]], meaning it can only equal certain discrete values, which correspond to different [[rotational energy]] states.  When a particle loses angular momentum, it is said to have transitioned to a lower rotational energy state.  Likewise, when a particle gains angular momentum, a positive rotational transition is said to have occurred.

Rotational transitions are important in physics due to the unique [[spectral lines]] that result. Because there is a net gain or loss of energy during a transition, [[electromagnetic radiation]] of a particular [[frequency]] must be absorbed or emitted. This forms [[spectral line]]s at that frequency which can be detected with a [[spectrometer]], as in [[rotational spectroscopy]] or [[Raman spectroscopy]].