Structural Isomers of Ti2O4 and Zr2O4 Anions Identified by Slow Photoelectron Velocity-Map Imaging Spectroscopy

High-resolution anion photoelectron spectra are reported for the group 4 metal dioxide clusters Ti2O4- and Zr2O4-. Slow photoelectron velocity-map imaging (SEVI) spectroscopy of cryogenically cooled, mass-selected anions yields photoelectron spectra with submillielectronvolt resolution, revealing extensive and well-resolved vibrational progressions. By comparison of the spectra with Franck-Condon Ti2O4- and Zr2O4- anions, respectively. Minor contributions from the C-2h isomer of Ti2O4- and the C-2v isomer of Zr2O4- are also seen. The SEVI spectra yield upper bounds for the adiabatic detachment energies, as well as vibrational frequencies for various modes of the neutral Ti2O4 and Zr2O4 species.