Ultraviolet photoelectron spectroscopy of molybdenum and molybdenum monoxide anions

The 351 nm photoelectron spectra of Mo-and MoO- have been measured. The electron affinity of atomic molybdenum is 0.748(2) eV and that of molybdenum monoxide is 1.290(6) eV. The term energies of several MoO electronic states not previously observed are obtained and compared with ab initio predictions. The ground state of MoO is confirmed to have 5II symmetry and the term energy of the 3II excited state, 10 179(20) cm21, closely matches calculations. The ground state of MoO2 is a 4P state with a vibrational frequency of 810(40) cm-1. The first excited state of molybdenum monoxide is tentatively assigned as a 3? state with T0=621(50) cm21. At least one state, possibly a 5?+ state, lies 8000(500) cm-1 above the ground state, and a 5?- state is observed at 11 590(60) cm-1 above the ground state. The separations of spin?orbit levels for the MoO X 5II, 3II, and 3? states are 169(30), 410(20), and 2720(20) cm-1, respectively. The vibrational frequencies of the 3II and 3? states are found to be 600(20) and 1000(20) cm-1, respectively. These observations give new insight into the Mo?O bond.