Where collision rate ZAB has unit mole/L/s (M/s), NA is Avogadro's number, molar concentration [A] and [B] have unit mole/L (M), relative diffusion constant Dr has unit m 2 /s, area of cross-section A has unit m 2 , fraction of effective cross-section area 𝛽 is unitless, and rate constant kJC has unit M -1 s -1 .