A direct classical trajectory study of the acetone photodissociation on the triplet surface

Product energy distributions (PEDs) for the photodissociation of acetone at 266, 248, and 193 nm were evaluated by direct classical trajectory calculations on the lowest triplet potential energy surface. CASSCF(8,7) and MRCI+Q calculations were first performed to obtain a set of high-level ab initio data with which the semiempirical parameters were refined. The trajectories were initiated at the barrier, using two different microcanonical sampling methods. The results obtained for the excess energies corresponding to excitation at 266 and 248 nm are in good agreement with the experimental product energy partitioning, supporting a dissociation event taking place on the T-1 surface after intersystem crossing from the initially exited S-1 state. At 193 nm, the results obtained with the two sampling methods show significant discrepancies. The PEDs calculated with the anharmonic sampling procedure appear to be consistent with the experimental data. (C) 2003 American Institute of Physics.