A factor introduced into simple versions of the collision theory of reactions to take care of the fact that the reaction probability depends on the certain mutual orientations of the reactant molecules.
See also: collision frequency
PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 187 (https://doi.org/10.1351/pac199668010149)
PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2216 (https://doi.org/10.1351/pac199062112167)