Multireference coupled-cluster calculation of the dissociation energy profile of triplet ketene

Triplet ketene exhibits a steplike structure in the experimentally observed photodissociation rates, but its mechanism is still unknown despite many theoretical efforts. Here we revisit this problem by calculating the potential energy profile of triplet ketene with the Adamowicz and Mukherjee multireference coupled-cluster (MRCC) theories. At the MRCCSD level, the imaginary frequency of the dissociation barrier is calculated to be about 300i cm−1, which is slightly smaller than the previous estimates but is still much greater than the expected maximum value for reproducing the observed steps (100i cm−1). This implies that other types of mechanisms (including nonadiabatic ones) may be more plausible for the observed steps.