Franck–Condon principle

E4700

physical principle spectroscopic rule

The Franck–Condon principle is a rule in molecular spectroscopy that explains the intensity distribution of vibronic transitions by assuming electronic transitions occur much faster than nuclear motion, making vertical transitions between vibrational states most probable.

Aliases (2)

Franck–Condon factors ×2
Franck–Condon approximation ×1

Statements (46)

Predicate	Object
instanceOf	physical principle → spectroscopic rule →
appliesTo	electronic transitions in molecules → vibronic transitions →
assumes	electronic transitions are much faster than nuclear motion → nuclear coordinates do not change during the electronic transition → transition dipole moment is weakly dependent on nuclear coordinates →
basedOn	Born–Oppenheimer approximation →
concerns	nuclear configuration space → overlap integrals of initial and final vibrational states → transition probabilities between vibrational levels → vertical transitions between potential energy surfaces →
describes	intensity distribution of vibronic transitions →
explains	progressions in vibrational structure of spectra → relative intensities of vibronic lines → shape of electronic absorption bands → shape of electronic emission bands →
field	molecular physics → molecular spectroscopy → quantum chemistry →
implies	most probable transitions are vertical on a potential energy diagram → nuclei are effectively fixed during an electronic transition →
mathematicalFormulation	transition intensity proportional to square of vibrational overlap integral →
namedAfter	Edward Condon → James Franck →
predicts	intensity maxima near classical turning points of vibrational motion → most intense transition originates from the ground vibrational level → vibrational progressions when equilibrium geometries differ between states →
relatedTo	Born–Oppenheimer approximation → Herzberg–Teller approximation → Huang–Rhys factor → potential energy curve → transition dipole moment → vibronic coupling →
relates	spectral band intensities to Franck–Condon factors → transition probability to overlap of vibrational wavefunctions →
usedFor	analyzing photophysical processes in molecules → assigning vibrational structure in electronic spectra → estimating geometry changes upon electronic excitation →
usedIn	analysis of potential energy surfaces → computational spectroscopy → interpretation of molecular absorption spectra → interpretation of molecular fluorescence spectra → interpretation of phosphorescence spectra → photoelectron spectroscopy →
usesConcept	Franck–Condon factors →

Referenced by (8)

Subject (surface form when different)	Predicate
Herzberg–Teller approximation → Herzberg–Teller approximation ("Franck–Condon approximation") →	refines
Huang–Rhys factor → Huang–Rhys factor ("Franck–Condon factors") →	relatedTo
Edward Condon →	coFormulated
Edward Condon →	knownFor
Born–Oppenheimer approximation →	usedIn
Franck–Condon principle ("Franck–Condon factors") →	usesConcept