Experimental and theoretical study of the photoelectron spectra of MnOx-(x=1-3) clusters

We report a combined experimental and theoretical investigation of MnOx- an d MnOx(x = 1-3) clusters. Theoretically, geometrical configurations of vari ous isomers of the clusters were optimized and vertical detachment energies for the anions were evaluated. The ground state of MnO- was predicted to b e (5)Sigma(+), followed by an excited state ((7)Sigma(+)) 0.14 eV higher in energy. The ground state of MnO2- is B-5(2), with a B-3(1) isomer 0.15 eV higher. MnO3- is predicted to be a singlet D-3h cluster. Vibrationally reso lved photoelectron spectra of MnOx- were measured at several photon energie s and under various experimental conditions, and were interpreted based on the theoretical results. The electron affinities of MnO, MnO2, and MnO3 wer e determined to be 1.375 (0.010), 2.06 (0.03), and 3.335 (0.010), respectiv ely. Five excited states of MnO were observed and assigned using the theore tical results. The (7)Sigma(+) excited state of MnO- was found to be signif icantly populated and was distinguished from the ground state of the anion by temperature dependent studies. We observed two isomers for MnO2- and the detachment features from both isomers were assigned. Only one vibrationall y resolved band was observed for MnO3-, which corresponds to transitions fr om the ground state of MnO3- to that of MnO3. The combined experimental and theoretical studies allow us to elucidate the complicated electronic and g eometric structures of the various manganese oxide clusters and their anion s. (C) 2000 American Institute of Physics. [S0021-9606(00)00428-1].