Low-lying states of HfS+ and the ionization energy of HfS

► First spectroscopic characterization of HfS+. ► Molecular constants for the X2Σ+ ground state and 2Δ excited state of HfS+. ► Ionization energy of HfS determined to be 7.6788(2) eV. ► Ab initio electronic structure calculations for the ground and low-lying states of HfS+.