Non-Boltzmann nuclear spin state distribution produced in thermal or photochemical reactions, usually from colligation and diffusion, or disproportionation of radical pairs, and detected by
NMR spectroscopy by enhanced absorption or emission signals.
Sources:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1097 (https://doi.org/10.1351/pac199466051077)
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2232 (https://doi.org/10.1351/pac199668122223)