collision efficiency, B c

https://dx.doi.org/10.1351/goldbook.C01164
The collision efficiency, or de-energization efficiency, is defined by:
k −1 = B c k −1 sc
where k −1is the rate constant for a particular substance M when it brings about the de-energization process
C01164
and k −1 sc 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 B c 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