CH3COCH3 photodissociation was investigated using the CASSCF energy gradien
t techniques. After the acetone molecules are populated in the S-1 state by
photoexcitation at 193 nm, the intersystem crossing to the T-1 surface is
the most probable pathway for CH3COCH3 (S-1) deactivation. Relaxing to the
T-1 state, CH3COCH3 (T-1) first dissociates into H3CO ((2)A') and CH3 ((2)A
(2)") products, and then the CH3CO ((2)A') formed further easily dissociate
s into CH3 and CO. This stepwise mechanism is consistent with numerous expe
riments. (C) 2000 Published by Elsevier Science B.V.