Electronic structure and low-lying electronic states of Al3O and Al3O-:: Photoelectron spectrum of Al3O-

We have calculated the equilibrium geometries of the ground electronic state of Al3O and Al3O- using Hartree-Fock, density functional, and coupled-cluster doubles methods. These molecules are nominally equilateral triangles of Al atoms with an oxygen in the center which distort due to the Jahn-Teller effect. The calculated global minima had C-2v symmetry with (b(2))(1) B-2(2) and (b(2))(2) (1)A(1) configurations, respectively. The global minimum of the lowest triplet state of Al3O- was found to have D-3h symmetry With an (e')(2) (3)A(2)' electron configuration. While this was the lowest energy state of the molecule among D3h symmetry points, this triplet minimum had slightly higher energy than the (1)A(1) state at its C-2v global,minimum. The (1)A(1) (a(1))(2) and the B-1(2) (b(2))(1)(a(1))(1) configurations of Al3O- and the (2)A(1) (a(1))(1) configuration of Al3O lead to transition states of C-2v symmetry on the respective potential energy surfaces for pseudorotation. Using the CCD geometries of (b(2))(2) (1)A(1) and (e')(2) (3)A(2)' Al3O-, configuration interaction calculations have been performed to determine the low-lying vertical excited states of Al3O, and those results have been utilized to interpret the recently reported experimental photoelectron spectrum of Al3O-. On the basis of the present CI results, new assignments have been made for some of the peaks.