A theoretical study on the photodissociation mechanism of acetyl fluoride (CH3C(O)F) involving S0, S1, and T1 states

The dissociation potential energy surfaces of acetyl fluoride (CH3C(O)F) in the lowest three electronic states (S-0, S-1, and T-1) have been calculated at the CASPT2-f12/VTZ-f12 level of theory. Combining with the surface intersection points, four mechanistic channels have been elucidated, namely, intersystem crossing (ISC) to the T-1 state, internal conversion (IC) to the ground state, H-atom transfer, and direct dissociation along the S-1 pathway. Unlike other acetyl halides, it is found that the alpha-C-C bond cleavage in T-1 surface after ISC to yield ground-state products CH3((2)A') + COF((2)A') is the most probable mechanism upon the excitation at 248 nm, which agrees well with the experimental observation. Both the S-1 and T-1 potential energy surfaces are reported systematically for the first time. A comparison of the reactivity among CH3C(O)F, CH3C(O)Cl, CH3C(O)Br, CH3C(O)I and CH3C(O)CH3 has been made. (C) 2017 Elsevier B.V. All rights reserved.