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## Kasha's rule
## Additional recommended knowledgeKasha's rule is relevant in understanding the emission spectrum of an excited molecule. Upon absorbing a photon, a molecule in its electronic ground state (denoted The rule can be explained by reference to the Franck-Condon factors for transitions between the excited states. For a given pair of states, the Franck-Condon factor expresses the degree of overlap between their vibrational wavefunctions; the greater the overlap, the quicker the molecule can undergo transition from one state to the other. Overlap is greatest between electronic states whose vibrationless levels (for which the vibrational quantum number Exceptions to Kasha's rule arise when there are large energy gaps between excited states. An example is azulene, the classical explanation for this is that the Categories: Luminescence | Quantum chemistry |

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Kasha's_rule". A list of authors is available in Wikipedia. |