light-atom anomaly
A dynamical effect that arises for a process w
 hen the species A is light (e.g. a hydrogen atom) compared to B and C. The vibrational excitation of the product A–B is low, since the light atom A approaches to within the bonding distance of BC before the C atom retreats. The energy of reaction is therefore released as repulsion between A–B and C, with the result that there is translational excitation of the products.
PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 171 (