Adiabatic photoreactions potential energy surfaces

Photolysis of w-butanal, 3-methylbutanal and 3,3-dimethylbutanal in the gas phase at 298 K affords the products arising from Norrish I (decarbonylated alkenes) and Norrish n (acetaldehyde + alkenes) cleavage. Ab initio and DPT calculations suggest that both processes can occur from either the singlet or the triplet excited states. Molecular dynamics simulation on the photochemistry of pentanal has been studied by a semiempirical MRCI method. The results show that Norrish I and II photoreactions take place on the adiabatic triplet potential energy surface the former (34%) occurs within 10 picoseconds whereas the latter (66%) takes more than 20 picoseconds. ... 

An approximation stating that the motion of nuclei in ordinary molecular vibrations is slow relative to the motions of electrons. Thus, the nuclei can be held in fixed positions when doing calculations of electronic states. Such an assumption is useful in determining potential energy surfaces and is central in studying the quantum mechanical properties of molecules. See also Adiabatic Photoreaction Diabatic Photoreaction... 

Adiabatic photoreaction Within the Born-Oppenheimer approximation , a reaction of an excited state species that occurs on a single potential-energy surface . Compare diabatic photoreaction. 

Diabatic photoreaction 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. 

---