Ionization potentials of niobium cluster oxides

Abstract 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.