Dissociative Adsorption of Water on CaMn 4 O 5 Cationic Clusters.

Water splitting is catalyzed by photosystem II, which comprises an inorganic core (CaMn 4 O 5 ) and protein ligands. To understand the evolution of CaMn 4 O 5 after attaching water molecules, an isolated CaMn 4 O 5 + cluster was investigated using vibrational spectroscopy and density functional theory calculations. Computational findings suggest that when a water molecule adsorbs on the Ca atom through the O atom of water, one of the OH bonds forms a hydrogen bond with a μ-oxo bridge, which dissociates into two OH groups. This is consistent with the fact that no isomers with molecularly adsorbed water were experimentally observed.