collision efficiency, \(B_{\text{c}}\)

Synonym: de-energization efficiency
https://doi.org/10.1351/goldbook.C01164
The collision efficiency, or de-energization efficiency, is defined by: \[k_{\text{-1}} = B_{\text{c}}\ k_{\text{-1}}^{\text{sc}}\] where k-1 is the rate constant for a particular substance M when it brings about the de-energization process
C01164.png
and k-1sc is the corresponding rate constant for a reference molecule M r that de-energizes A* on every collision; that is, the reference molecule M r undergoes strong collisions, and by definition has a collision efficiency Bc of unity. The species A* is usually in a vibrationally-excited state, and A has energy less than that required for reaction to occur.
Source:
PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 159 (https://doi.org/10.1351/pac199668010149)