 This contrasting feature allows rovibronic transitions that might not be active in IR to be analyzed using Raman spectroscopy, as exemplified by the rule of mutual exclusion in centrosymmetric molecules.Transitions which have large Raman intensities often have weak IR intensities and vice versa.If a bond is strongly polarized, a small change in its length such as that which occurs during a vibration has only a small resultant effect on polarization.