Resonant photoelectron spectroscopy of Au2- via a Feshbach state using high-resolution photoelectron imaging

Photodetachment cross sections are measured across the detachment threshold of Au-2(-) between 1.90 and 2.02 eV using a tunable laser. In addition to obtaining a more accurate electron affinity for Au-2 (1.9393 +/- 0.0003 eV), we observe eight resonances above the detachment threshold, corresponding to excitations from the vibrational levels of the Au-2(-) ground state (X (2)Sigma(+)(u)) to those of a metastable excited state of Au-2(-) (or Feshbach resonances) at an excitation energy of 1.9717 +/- 0.0003 eV and a vibrational frequency of 129.1 +/- 1.5 cm(-1). High-resolution photoelectron spectra of Au-2(-) are obtained using photoelectron imaging to follow the autodetachment processes by tuning the detachment laser to all the eight Feshbach resonances. We observe significant non-Franck-Condon behaviors in the resonant photoelectron spectra due to autodetachment from a given vibrational level of the Feshbach state to selective vibrational levels of the neutral final state. Using the spectroscopic data for the ground states of Au-2(-) (X (2)Sigma(+)(u)) and Au-2 (X (1)Sigma(+)(g)), we estimate an equilibrium bond distance of 2.53 +/- 0.02 angstrom for the Feshbach state of Au-2(-) by simulating the Franck-Condon factors for the resonant excitation and autodetachment processes. (C) 2013 AIP Publishing LLC.