Influence of Cr doping on the stability and structure of small cobalt oxide clusters

The stability of mass-selected pure cobalt oxide and chromium doped cobalt oxide cluster cations, Co_nO_m⁺ and Co_n−1CrO_m⁺ (n = 2, 3; m = 2–6 and n = 4; m = 3–8), has been investigated using photodissociation mass spectrometry. Oxygen-rich Co_nO_m⁺ clusters (m ⩾ n + 1 for n = 2, 4 and m ⩾ n + 2 for n = 3) prefer to photodissociate via the loss of an oxygen molecule, whereas oxygen poorer clusters favor the evaporation of oxygen atoms. Substituting a single Co atom by a single Cr atom alters the dissociation behavior. All investigated Co_n−1CrO_m⁺ clusters, except CoCrO₂⁺ and CoCrO₃⁺, prefer to decay by eliminating a neutral oxygen molecule. Co₂O₂⁺, Co₄O₃⁺, Co₄O₄⁺, and CoCrO₂⁺ are found to be relatively difficult to dissociate and appear as fragmentation product of several larger clusters, suggesting that they are particularly stable. The geometric structures of pure and Cr doped cobalt oxide species are studied using density functional theory calculations. Dissociation energies for different evaporation channels are calculated and compared with the experimental observations. The influence of the dopant atom on the structure and the stability of the clusters is discussed