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), produce by laser vaporization, with various gas samples (CH₄, N₂, H₂, 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.