Chemisorption of Nitrogen Monoxide on Size-Selected Cobalt Cluster Ions

摘要

Collisional reactions of NO with Co_n~+(n=2-10)were studied by measuring the absolute cross sections for creating the product ions in a beam-gas geometry at different collision energies and internal temperatures of Co_n~+The dominant reaction is chemisorption of NO on Co/(formation of Co_nNO~+and Co_(n-1)NO~+).As n increases,the chemisorption cross section starts to rise sharply at n=4 and soon reaches the highest possible value,which is the Langevin cross section.The chemisorption cross section practically does not change with the internal temperature,while the branching fraction for the production of Co_nNO~+with respect to the sum of Co_nNO~+and Co_(n-1)NO~+decreases with the internal temperature in the size range of n=6-10.A statistical model based on the RRK theory explains the dependences of the chemisorption cross section and the branching fraction on the size(n),the collision energy,and the internal temperature.The energies of the NO chemisorption derived from the dependences of the chemisorption cross section and the branching fraction on the collision energy and the internal temperature show that(1)the NO chemisorption is dissociative for n>4 and(2)more than one isomer is involved in the chemisorption of NO on Co_9~+.