The cyclic MO2 (M=Al, Ga) systems: CCSD(T) and DFT studies of their structures, harmonic vibrational frequencies, and dissociation energies

The AlO2 and GaO2 superoxides are the primary products of the reaction of Al, or Ga, with O2 in cryogenic matrices. CCSD(T) and DFT calculations using 6-311+G(3df) and 6-311+G(2df) basis for AlO2 and GaO2, respectively, have been performed. The calculated equilibrium geometries, harmonic frequencies, and dissociation energies are presented. Each system possesses a 2A2 ground state. The CCSD(T) calculations yield dissociation energies of 65 and 51 kcal/mol, respectively. DFT yields similar results. Comparison with existing experimental and theoretical data are made. Both the DFT and the single reference CCSD(T) methods overcome the symmetry breaking problems encountered in previous theoretical studies.