Photoelectron spectroscopy of anions at 118.2nm: Observation of high electron binding energies in superhalogens MCl4− (M=Sc, Y, La)

High energy photon is needed for photoelectron spectroscopy (PES) of anions with high electron binding energies, such as superhalogens and O-rich metal oxide clusters. The highest energy photon used for anion PES in the laboratory has been 157nm (7.866eV) from F2 eximer lasers. Here, we report an anion PES experiment using coherent vacuum ultraviolet radiation at 118.2nm (10.488eV) by tripling the third harmonic output (355nm) of a Nd:YAG laser in a Xe∕Ar cell. Our study focuses on a set of superhalogen species, MCl4− (M=Sc, Y, La), which were expected to possess very high electron binding energies. While the 157nm photon can only access the ground state detachment features for these species, more transitions to the excited states at binding energies higher than 8eV are observed at 118.2nm. The adiabatic detachment energies are shown to be, 6.84, 7.02, and 7.03eV for ScCl4−, YCl4−, and LaCl4−eV, respectively, whereas their corresponding vertical detachment energies are measured to be 7.14, 7.31, and 7.38eV.