- AMER CHEMICAL SOC
Reactions of copper cluster cations doped with an early transition metal atom, CunTi+ (n = 4-15) and CunV+ (n = 5-14, 16), with NO and O-2 were investigated at a near-thermal collision energy using a guided ion beam tandem mass spectrometer. Most of the clusters adsorb NO and O-2 under single collision conditions, and this reaction is often followed by the release of Cu atoms. For both Ti- and V-doped Cu clusters, the total cross sections for the reaction with NO increase gradually with the cluster size up to n approximate to 11 and then decrease rapidly, whereas those with O-2 are almost constant in n <= 12 and then decrease. The size dependence of the reactivity toward NO is found to correlate with that of the adsorption energy calculated by the density functional theory method; Cur,Ti+ clusters exhibit the larger reaction cross sections when they have the larger adsorption energies. The calculations of CunTi+ also show that a structural transition from a Ti- exposed structure to Ti-encapsulated one occurs around n = 12. This indicates that a geometric property of the clusters, i.e., the position of the dopant atom, is a determining factor of reactivity. In addition, the Ti- and V-doping dramatically improves the reactivity of Cu cluster cations toward NO but it does not affect that toward O-2 significantly. As a result, most of the Ti- and V-doped Cu clusters are more reactive toward NO than toward O-2. We also studied the multiple-collision reaction of Cu7Ti+ with NO and obtained the cluster dioxide, Cu3TiO2+, as a product ion, which suggests that the dissociation of NO and the subsequent formation/release of N-2 take place.
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