STRUCTURAL TRANSITION IN BARIUM SUBOXIDE CLUSTERS

Ionization potentials of BanOm clusters (2 less than or equal to n les s than or equal to 13, m less than or equal to n) have been measured b y one-photon ionization. Beyond n greater than or equal to 8, a specif ic structural transition is observed when the oxygen/barium ratio incr eases. A tentative interpretation based on the interplay between Ba-Ba and Ba-O bindings and its consequences in terms of oxygen atom locali zation and stability of the bare barium skeleton are discussed. A comp arison with mixed clusters involving other electronegative elements is approached. Combined with metallic atoms (alkali, alkaline-earth), ox ygen seems to have a specific behavior which excludes segregation.