Within the Born–Oppenheimer approximation, a reaction beginning on one excited state 'potential-energy surface' and ending, as a result of radiationless transition, on another surface, usually that of the ground state. Also called non-adiabatic.
See also: adiabatic photoreaction
Source:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2235 (https://doi.org/10.1351/pac199668122223)