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

We report a combined experimental and theoretical investigation of MnOx- and MnOx(x = 1-3) clusters. Theoretically, geometrical configurations of various isomers of the clusters were optimized and vertical detachment energies for the anions were evaluated. The ground state of MnO- was predicted to be (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 resolved photoelectron spectra of MnOx- were measured at several photon energies and under various experimental conditions, and were interpreted based on the theoretical results. The electron affinities of MnO, MnO2, and MnO3 were determined to be 1.375 (0.010), 2.06 (0.03), and 3.335 (0.010), respectively. Five excited states of MnO were observed and assigned using the theoretical results. The (7)Sigma(+) excited state of MnO- was found to be significantly 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 vibrationally resolved band was observed for MnO3-, which corresponds to transitions from the ground state of MnO3- to that of MnO3. The combined experimental and theoretical studies allow us to elucidate the complicated electronic and geometric structures of the various manganese oxide clusters and their anions. (C) 2000 American Institute of Physics. [S0021-9606(00)00428-1].