Photochemical process leading to the formation of a cyclobutane from two identical @A00224@, i.e., from the @AT07318@ of an @E01994@ alkene to a ground-state alkene.
Source: PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 301 [Terms] [Paper]