Dissociative chemisorption of molecular hydrogen on niobium cluster ions. A supersonic cluster beam FT-ICR experiment

Positive cluster ions of niobium produced by laser vaporization and cooled by supersonic expansion have been injected into the ion trap of a Fourier transform ion cyclotron resonance spectrometer. By use of this new technique, the relative rates of H/sub 2/ dissociative chemisorption were measured for the clusters Nb/sub 7//sup +/, Nb/sub 8//sup +/, and Nb/sub 9//sup +/. In striking agreement with earlier studies on the neutral clusters, Nb/sub 7//sup +/ was found to be far more reactive than either Nb/sub 8/ or Nb/sub 9//sup +/. Such a close correspondence in reactivity patterns between the positive and neutral clusters is inconsistent with a simple electrostatic model of the dissociative chemisorption process.