Vibrationally resolved photoelectron spectroscopy of AlO- and AlO2-

Vibrationally resolved photoelectron spectra of AlO- and AlO2- have been obtained at two photon energies, 3.49 and 4.66 eV. Both the ground and first excited states are observed for AlO. The spectrum of AlO2- can only be obtained at the higher photon energy due to the high electron affinity (EA) of AlO2. The electron affinities of AlO and AlO2 are measured to be 2.60(1) and 4.23(1) eV, respectively. The rather high EAs for both molecules are consistent with the fact that AlO- and AlO2- anions are closed-shell, isoelectronic with SiO and SiO2, respectively. The vibrational frequency of the AlO- anion is observed to be 900 (50) cm(-1). The vibrational frequencies and excitation energy obtained for AlO agree well with previous optical measurements. The totally symmetric vibrational frequency is observed to be 750 (40) cm(-1) for AlO2 and 680 (60) cm(-1) for AlO2-. The AlO2 molecule, as well as AlO2-, is concluded to have a linear OAlO structure from the spectroscopic information obtained.