An ab initio study of potential energy surfaces of CH3COCN dissociation on the low-lying states

The C–CH3 and C–CN bond dissociations of CH3COCN on S1 and T1 surfaces are studied at the CAS(8,7)/cc-pVDZ level. The results show that the intersystem crossing from S1 to T1 is a favorable pathway of S1 deactivation. Once on the T1 surface, the system can dissociate adiabatically to CH3 (X̃)+OCCN (X̃) or CN (X̃)+CH3CO (X̃), but the former has some preference over the latter. This mechanism is consistent with Chengʹs presumption deduced from the experimental facts and theoretical considerations. A comparison with other asymmetrically substituted carbonyl compounds suggests that the selectivity of the α-bond cleavage is mainly dependent on the mechanism of dissociation.