Electromagnatic Rotation :- Rotational Selection rules

 Rotational Selection rules:

1. Transitions with ΔJ=±1 are allowed;

Photons do not have any mass, but they have angular momentum. The conservation of 

angular momentum is the fundamental criteria for spectroscopic transitions. As a 

result, the total angular momentum has to be conserved after a molecule absorbs or 

emits a photon. The rotational selection rule relies on the fact that photon has one unit 

of quantized angular momentum. During the photon emission and absorption process, 

the angular moment J cannot change by more than one unit.