CASPT2 Study of Photodissociation Pathways of Ketene

The mechanism of various photodissociation channels of ketene involving the three lowest singlet states (S-0, S-1, and S-2) and the three lowest triplet states (T-1, T-2, and T-3) was investigated by means of the (MS-)CAS(8e,8o)PT2/6-31+G* method. Stationary structures, i.e., global minima (GMs), local minima (LMs), transition states (TSs), minimum energy conical intersections (MECIs), and minima on seam of crossing (MSXs), were explored systematically by the global reaction route mapping (GRRM) strategy. On the basis of these structures, we discussed related dissociation channels starting from S2 that have been studied experimentally with 193-215 nm excitation wavelength. Five working pathways were found for relaxation to the low-lying S-0, S-1, and T-1 potential energy surfaces (PESs) from the Franck-Condon region of S-2, and the relaxation is expected to occur very quickly. On these low-lying states, five dissociation channels are open: three CH2 + CO channels for different CH2 electronic states, H + HCCO, and H-2 + C2O. Pathways for all of these five channels were identified and discussed, including new minor paths leading to H-2 + C2O.