Sources: Green Book, 2nd ed., p. 56 [Terms] [Book] PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 160 [Terms] [Paper]
See also: PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2181 [Terms] [Paper]