initiation

https://doi.org/10.1351/goldbook.I03042
A reaction or process generating free @R05066@ (or some other @R05180@ @R05171@) which then induce a @C00960@. For example, in the chlorination of @A00222@ by a radical mechanism the initiation step is the @D01801@ of molecular chlorine.
Sources:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1125 [Terms] [Paper]
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 169 [Terms] [Paper]