Mechanisms of Complete Dissociation of CO on Iron Clusters.

Dissociation of CO on iron clusters was studied by using semilocal density functional theory and basis sets of triple-zeta quality. Fe , Fe , and Fe clusters were selected as the representative host clusters. When searching for isomers of Fe CO , n=2, 4 and 16 corresponding to carbon dioxide attachment to the host clusters, its reduction to O and CO, and to the complete dissociation, it was found that the total spin magnetic moments of the lowest energy states of the isomers are often quenched with respect to those of initial reagents Fe +CO . Dissociation pathways of the Fe +CO , Fe +CO , and Fe +CO reactions contain several transition states separated by the local minima states; therefore, a natural question is where do the spin flips occur? Since lifetimes of magnetically excited states were shown to be of the order of 100 fs, the search for the CO dissociation pathways was performed under the assumption that magnetic deexcitation may occur at the intermediate local minima. Two dissociation pathways were obtained for each Fe +CO reaction using the gradient-based methods. It was found that the Fe +CO reaction is endothermic with respect to both reduction and complete dissociation of CO , whereas the Fe +CO and Fe +CO reactions are exothermic to both reduction and complete dissociation of carbon dioxide. The CO reduction was found to be more favorable than its complete dissociation in the Fe case.