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].