Classically, the Franck–Condon principle is the approximation that an electronic transition
is most likely to occur without changes in the positions of the nuclei in the molecular
entity and its environment. The resulting state is called a Franck–Condon state, and
the transition involved, a vertical transition. The quantum mechanical formulation
of this principle is that the intensity of a
vibronic transition is proportional to the square of the
overlap integral between the vibrational wavefunctions of the two states that are involved in the
transition.
Source:
PAC, 1996, 68, 2223
(Glossary of terms used in photochemistry (IUPAC Recommendations 1996))
on page 2243
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.
