Electronic and vibrational structure of transition metal trimers: Photoelectron spectra of Ni−3, Pd−3, and Pt−3

The transition metal trimer anions Ni−3, Pd−3, and Pt−3 are prepared in a flowing afterglow ion source with a cold cathode dc discharge. The low-lying electronic states of the neutral trimers are probed by 488 nm negative ion photoelectron spectroscopy at an electron kinetic energy resolution of 5–12 meV. Each trimer exhibits multiple low-lying electronic states. Vibrational progressions are observed in tripalladium and triplatinum. The adiabatic electron affinities are found to be EA(Ni3)=1.41±0.05 eV, EA(Pd3)≲1.5±0.1 eV, and EA (Pt3)=1.87±0.02 eV.