AL3OY (Y=0-5) CLUSTERS - SEQUENTIAL OXIDATION, METAL-TO-OXIDE TRANSFORMATION, AND PHOTOISOMERIZATION

Photoelectron spectra of a series of Al3Oy- clusters (y=0-5) are prese nted at several photon energies: 532, 355, 266, and 193 nm. The electr on affinities and low-lying electronic states of the Al3Oy clusters ar e reported. The photoelectron spectra clearly reveal a sequential oxid ation behavior and how the electronic structure of the clusters evolve s from that of a metal cluster at Al, to that of a complete oxide clus ter at Al3O5: Two valence electrons of Al-3 are observed to be transfe rred to each additional O atom until Al3O5, where all the nine valence electrons of Al-3 are transferred to the five O atoms. The anion, Al3 O5, which can be viewed as (Al3+)(3)(O2-)(5), is found to be a closed shell cluster, yielding an extremely high electron affinity for Al3O5 (4.92 eV). The electron affinities of the remaining clusters are: 1.90 (Al-3), 1.57 eV (Al3O), 2.18 eV (Al3O2), 2.80 eV (Al3O3), and 3.58 eV (Al3O3) An electronic excited state of Al; is also observed at 0.40 e V above the Al; ground state. Isomers are observed for all the oxide c lusters with lower electron affinities; Particularly, vibrational stru ctures are observed for the two isomers of Al3O3-, as well as a photoi somerization process between the two isomers. The structure and bondin g of the oxide clusters are discussed based on the experimental data a nd the known structures for Al-3 and Al3O. (C) 1998 American Institute of Physics.