Photoelectron spectroscopy of group IV heavy metal dimers: Sn−2, Pb−2, and SnPb−

Negative ion photoelectron spectra of Sn−2, SnPb−, and Pb−2 are presented for electron binding energies up to 3.35 eV. Each spectrum exhibits multiple electronic bands, most of which contain resolved vibrational structure. Franck-Condon analyses yield spectroscopic parameters (re, ωe, and Te) for the anion ground states and the neutral excited states. Adiabatic electron affinities are determined to be: EA(Sn2)=1.962±0.010 eV, EA(Pb2)=1.366±0.010 eV, and EA(SnPb)=1.569±0.008 eV. The anion dissociation energies D0(Sn−2) and D0(Pb−2) are derived from the electron affinities and the neutral dissociation energies. For SnPb−, the dissociation energy difference D0(SnPb−)−D0(SnPb) is precisely measured. Based on the present data, previous experiments and ab initio calculations, we assign most of the observed bands to the corresponding neutral low-lying electronic states.