High-resolution spectroscopy of Ag+2 via long-lived ZEKE states

We report on mass-analyzed ZEKE spectra of Ag+2 via resonance-enhanced two-color excitation. To the best of our knowledge, this is the first metal dimer and at the same time the heaviest system (218 amu) ever investigated by mass-analyzed ZEKE. The adiabatic ionization potential, vibrational energies for v+ = 1, 2, 3 and 4 as well as the vibrational constants ωe, ωeχe of the ionic ground state X2Σ+g are determined with high accuracy. The surprising intensity pattern of vibrational progressions cannot be rationalized within a Franck—Condon picture and points to the unique properties of ZEKE states.