Franck–Condon vibrational overlap
An electronic transition is fast relative to nuclear motion, so its initial nuclear coordinates are approximately unchanged during the transition.
Key knowledge
An electronic transition is fast relative to nuclear motion, so its initial nuclear coordinates are approximately unchanged during the transition. Under the Condon approximation, the electronic transition moment varies little across the relevant nuclear coordinates and the vibrational contribution to intensity depends on the squared overlap of initial and final vibrational wavefunctions. This explains progressions without assigning every band solely from an energy gap.
Values and equations
FCv′v = |∫ χv′*(Q) χv(Q) dQ|²
- FCv′v
- dimensionless vibrational overlap factor 1
- χv,χv′
- normalized initial and final vibrational wavefunctions coordinate-normalization dependent
- Q
- nuclear coordinate or set of coordinates integrated over the same measure coordinate dependent
Conditions and scope
- Condon factorization is approximate; vibronic coupling can change intensities and selection rules.
- The strongest band is not guaranteed to connect potential minima or any one classical turning point.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Read vertical-transition and vibrational-overlap argument on pp.4–5; used modulus squared and explicit Condon condition rather than universal turning-point claims.
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Entry details
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- uni-chem-franck-condon
- Revision
- core.1
- Structured reference record
- University core expansion