High-resolution anion photoelectron spectra of TiO2−, ZrO2−, and HfO2− obtained by slow electron velocity-map imaging
High-resolution anion photoelectron spectra of the Group 4 metal dioxides TiO2−, ZrO2−, and HfO2− are reported, using slow electron velocity-map imaging (SEVI) combined with ion trapping and cryogenic cooling. The resulting spectra exhibit sub-meV resolution with no congestion from hot bands. Electron affinities are obtained with greater precision than in previous photodetachment experiments, with values of 1.5892(5) eV, 1.6397(5) eV, and 2.1045(5) eV, for TiO2, ZrO2, and HfO2, respectively. We obtain precise values for all of the vibrational frequencies of the neutral 1A1 ground states, except for the ν3 mode of HfO2. Weak activity observed in the forbidden ν3 mode for TiO2 and ZrO2 is attributed to Herzberg–Teller coupling to the Ã2B2 excited state.