High-resolution anion photoelectron spectra of TiO2−, ZrO2−, and HfO2− obtained by slow electron velocity-map imaging

Abstract

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 òB₂ excited state.