Internal conversion (chemistry)

Internal conversion ( engl. internal conversion, "IC" ) is a term used in photochemistry and spectroscopy. It refers to the non-radiative transition from an electronically excited state to another, without changing the multiplicity ( no spin flip ). If changes the multiplicity, it is, however, an intersystem crossing. Internal transformations occur with the highest probability in the vicinity of intersections of two potential curves. Heard the second potential curve to an unbound continuum state, dissociation occurs.

Otherwise, the transition is usually done with a vibronically excited state which subsequently, releasing energy by collisions with surrounding particles can radiationless transition to the ground state. Since large molecules have more vibrational modes than small, they are more likely for such a transition A., is higher. An overview of the possible transitions are the Jablonski diagram.

The melanin of the skin, and the DNA use the internal conversion, to convert the harmful for the organism UV radiation into harmless heat. This ultrafast internal conversion is responsible for the excellent UV protection of these large natural molecules.

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Fast internal conversion in DNA

• Spectroscopy
• Photochemistry