Al 3 O y (y=0–5) clusters: Sequential oxidation, metal-to-oxide transformation, and photoisomerization

Photoelectron spectra of a series of Al3Oy− clusters (y=0–5) are presented at several photon energies: 532, 355, 266, and 193 nm. The electron affinities and low-lying electronic states of the Al3Oy clusters are reported. The photoelectron spectra clearly reveal a sequential oxidation behavior and how the electronic structure of the clusters evolves from that of a metal cluster at Al3 to that of a complete oxide cluster at Al3O5: Two valence electrons of Al3 are observed to be transferred to each additional O atom until Al3O5, where all the nine valence electrons of Al3 are transferred to the five O atoms. The anion, Al3O5−, 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 (Al3), 1.57 eV (Al3O), 2.18 eV (Al3O2), 2.80 eV (Al3O3), and 3.58 eV (Al3O4). An electronic excited state of Al3− is also observed at 0.40 eV above the Al3− ground state. Isomers are o...