Charge dependence of chemisorption patterns for transition metal clusters

A method is presented for the measurement of the chemisorptive reactivity of transition metal cluster ions at near room temperature. Similar to a technique introduced previously for neutral clusters [Rev. Sci. Instrum. 56, 2123 (1985)], this cluster ion method utilizes a fast‐flow reactor attached to a supersonic, laser vaporization metal cluster source, followed by time‐of‐flight mass spectral analysis of the cluster ions as a function of reactant concentration. Results are presented for clusters of cobalt and niobium in the 1–22 atom size range for their chemisorptive reactions with CO, CO2, and N2. Both Nb+n and Co+n clusters displayed chemical reactivity that is remarkably similar to that of the corresponding neutral clusters. For both charge states of each metal, CO was found to chemisorb with a rate which varied in a slow, monotonically increasing fashion with cluster size. The chemisorption rate of N2 and CO2, on the other hand, was found to be significantly slower than that of CO and sharply depen...