Photoelectron spectroscopy and zero electron kinetic energy spectroscopy of germanium cluster anions

Anion photoelectron spectra of Ge-n(-), n=2-15, have been measured using an incident photon energy of 4.66 eV. In addition, the spectra of Ge-2(-), Ge-3(-), and Ge-4(-) have been measured at photon energies of 3.49 and 2.98 eV. From these spectra the electron affinity of the corresponding neutral cluster has been determined. Vibrational frequencies and term values for several electronic states of Ge-2(-) and Ge-3(-) have been determined. Vibrational structure in the B-3(3u) excited state of Ge-4 has been resolved using zero electron kinetic energy (ZEKE) photoelectron spectroscopy. The assignment of the spectra of Ge-3(-) and Ge-4(-) is facilitated by a comparison to the similar spectra of Si-3(-) and Si-4(-), respectively. The spectra of the larger clusters, Ge-n(-), n=5-15, are characterized by many broad structureless features which indicate the presence of multiple electronic transitions. Several of these were assigned based on comparison with previous ab initio calculations on germanium and silicon clusters. (C) 1996 American Institute of Physics.