Norrish Type II photoreaction

https://doi.org/10.1351/goldbook.N04218

intramolecular abstraction of a γ-hydrogen by an excited carbonyl compound to produce a 1,4-diradical as a primary photoproduct.

Note:
An example is:

N04218.png

Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 375 (https://doi.org/10.1351/pac200779030293)