REACTIVITY OF POSITIVELY CHARGED COBALT CLUSTER IONS WITH CH4, N2, H2, C2H4, AND C2H2

Reactivity of positively charged cobalt cluster ions (Co(n)+, n = 2-22), produced by laser vaporization, with various gas samples CH4, N2, H-2, C2H4, and C2H2) were systematically investigated by using a fast-flow reactor. The reactivity of Co(n)+ with the various gas samples is qualitatively consistent with the adsorption rate of the gas to cobalt metal surfaces. Co(n)+ highly reacts with C2H2 as characterized by the adsorption rate to metal surfaces, and it indicates no size dependence. In contrast, the reactions of Co(n)+ with the other gas samples indicate a similar cluster size dependence; at n = 4, 5, and 10-15, Co(n)+ highly reacts. The difference can be explained by the amount of the activation energy for chemisorption reaction. Compared with neutral cobalt clusters, the size dependence is almost similar except for Co4+ and Co5+. The reactivity enhancement of Co4+ and Co5+ indicates that the cobalt cluster ions are presumed to have an active site for chemisorption at n = 4 and 5, induced by the influence of positive charge.