Time-dependent density functional theory study of Fe2(CO)9 low-lying electronic excited states.

The valence electronic excited states of Fe2(CO)9 have been studied using the time-dependent density functional theory (TDDFT). Both tribridged D3h and monobridged C2v structures have been considered, and the structure of selected low-lying singlet and triplet excited states have been optimized on the basis of the TDDFT analytical gradient. Optimized excited-state geometries are used to obtain an insight into certain aspects of the Fe2(CO)9 photochemistry. The Fe2(CO)9 (D3h) first triplet and second singlet excited states are unbound with respect to dibridged Fe2(CO)8 + CO, and the first two monobridged Fe2(CO)9 (C2v) singlet states are unbound with respect to the Fe(CO)5 + Fe(CO)4 dissociation. These results are discussed in light of the experimental data available.