collision number

https://doi.org/10.1351/goldbook.C01169
Now called collision density.
Sources:
Green Book, 2nd ed., p. 56 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)
PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 160 (https://doi.org/10.1351/pac199668010149)