entrance channel

https://doi.org/10.1351/goldbook.E02148
The region of a @[email protected] or hypersurface that corresponds to molecular configurations that are closer in geometry to those of the reactants than to those of the products.
Source:
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 165 [Terms] [Paper]