precursor complex

https://doi.org/10.1351/goldbook.P04806
May either indicate an encounter complex or a collision complex, but furthermore implies that this complex undergoes a reaction (e.g. electron transfer).
Source:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2266 (https://doi.org/10.1351/pac199668122223)