Ground and excited states of Al2O2 and its anion

CASSCF, MRMP2, MR-CISD, CCSD(T) and CR-CCSD(T) theories were adopted to study the isomers of Al2O2 and its anion. CR-CCSD(T) and MR-CISD consistently indicate that the linear isomer 2 is the ground state, which is consistent with matrix isolation experiments. All three peaks at 1.88, 2.37 and 5.1 eV in the photoelectron spectra can be readily assigned as 2B3u → 1Ag, 2B3u → 3B3u and 2B3u → 1B3u of isomer 1, respectively indicating that the electronic states of isomer 1 are in better agreements with the photoelectron detachment spectra. These contradicting results may imply that the major isomer of Al2O2 can depend on the experimental conditions.