Photoelectron spectroscopy of the molecular anions, ZrO−, HfO−, HfHO−, and HfO2H−

Negative ion photoelectron spectra of ZrO−, HfO−, HfHO−, and HfO2H− are reported. Even though zirconium- and hafnium-containing molecules typically exhibit similar chemistries, the negative ion photoelectron spectral profiles of ZrO− and HfO− are dramatically different from one another. By comparing these data with relevant theoretical and experimental studies, as well as by using insights drawn from atomic spectra, spin-orbit interactions, and relativistic effects, the photodetachment transitions in the spectra of ZrO− and HfO− were assigned. As a result, the electron affinities of ZrO and HfO were determined to be 1.26 ± 0.05 eV and 0.60 ± 0.05 eV, respectively. The anion photoelectron spectra of HfHO− and HfO2H− are similar to one another and their structural connectivities are likely to be H–Hf–O− and O–Hf–OH−, respectively. The electron affinities of HfHO and HfO2H are 1.70 ± 0.05 eV and 1.73 ± 0.05 eV, respectively.