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 stat e of Al3O and Al3O- using Hartree-Fock, density functional, and coupled-clu ster doubles methods. These molecules are nominally equilateral triangles o f Al atoms with an oxygen in the center which distort due to the Jahn-Telle r 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 a n (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. T he (1)A(1) (a(1))(2) and the B-1(2) (b(2))(1)(a(1))(1) configurations of Al 3O- and the (2)A(1) (a(1))(1) configuration of Al3O lead to transition stat es of C-2v symmetry on the respective potential energy surfaces for pseudor otation. 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 deter mine 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.