Theoretical Interpretation of the Photoelectron Spectra of Al3O2-and Al3O3-

Abstract

Hartree−Fock (HF) and density functional theory (DFT) calculations have been used to determine the equilibrium geometries of the ground electronic state of Al3O2, Al3O3, and their corresponding negative ions. The calculated global minimum for Al3O2 has a “vee” shape of C2v symmetry with a (a1)1 2A1 configuration. A kite-shaped structure of C2v symmetry has been obtained as a local minimum with a (b2)1 2B2 configuration. The corresponding negative ions have also been found to be global and local minima, respectively, with (a1)2 1A1 and (b2)2 1A1 electron configurations. A higher energy trigonal bipyramidal D3h structure has been found with a 1A1‘ (e‘)4 electron configuration. For Al3O3-, the calculated global minimum has a bicyclic rectangular shape of C2v symmetry with a (b2)2 1A1 configuration, whereas the corresponding neutral Al3O3 with a (b2)1 2B2 configuration has been found to be a local minimum. On the other hand, a kite shape of C2v symmetry with a (a1)1 2A1 configuration has been found to be the global minimum of neutral Al3O3. The lowest triplet state of Al3O3- had a hexagonal shape of D3h symmetry with a (e‘)2 configuration. This triplet minimum has slightly higher energy than either of the singlet minima. Configuration interaction (CI) calculations have been performed using the DFT optimized geometries for the two lowest energy structures of Al3O2- and the two lowest energy structures of Al3O3- to determine the low lying vertical excited states of Al3O2 and Al3O3. Those results have been utilized to interpret the recently reported experimental photoelectron spectra of Al3O2- and Al3O3-. On the basis of the present CI results, the symmetry of the states involved in the photoelectron peaks have been assigned for both spectra.