IONIZATION-POTENTIALS OF NIOBIUM CLUSTER OXIDES

Threshold ionization potentials have been determined for a number of niobium cluster oxides, Nb(n)O(m), n = 3-20, m = 1-5. For most values of n, the ionization potential is only weakly dependent on the number of oxygen atoms. However, large changes with m occur for clusters with nine niobium atoms. We attribute this behavior to a geometrical effect and suggest that an ''inside/outside'' isomerization occurs in this size range. It is also suggested that niobium clusters which are more reactive to dissociative chemisorption of deuterium have surface atoms of higher coordination number.