Ab initio studies of stationary points of the Al2O3 molecule

We report a theoretical ab initio investigation on energetically low-lying stationary points of the Al2O3 molecular system. The calculations were performed at the Hartree-Fock (HF) and second-order Moller-Plesset (MP2) frozen core level of approximation using the standard 6-31G(d) basis set. Several isomeric singlet as well as higher spin states of Al2O3 which lie close to each other within an energy range of about 8 eV (at MP2) are characterised. The lowest of these stationary points is in fact a triplet state of planar C-2v symmetry. It is by 0.08 eV (MP2) lower than the often discussed linear D-infinity h singlet state. Atomisation energies for all species are quite large showing that the system is strongly bound. Energies, harmonic vibrational modes, and geometric parameters are compared with the results of earlier work by Solomonik and Sliznev [1] Nemukhin and Weinhold [2], Andrews et al. [3] and Desai et al. [4]. Based on our calculations we give a tentative assignment of some selected vibrational wave numbers and an interpretation of some features of the photoelectron spectrum.