Accurate electron affinity of atomic rhodium and fine structure of its anion

Rhodium (Rh) is a rare and expensive metal, mainly used as a catalyst. Investigating its electronic structure aids in elucidating the mechanisms that govern catalytic reactions. In this work, we employed the high-resolution slow-electron velocity-map imaging (SEVI) method to measure the electron affinity (EA) of Rh and the electronic structure of its atomic anion Rh⁻. The EA of the Rh atom was determined to be 9216.8(4) cm⁻¹ or 1.14273(5) eV, representing a fourfold enhancement in precision over the previous best result. Moreover, the energy levels of Rh⁻ were measured to be 0.41178(15) eV (³F₂) and 0.28668(7) eV (³F₃) above the ground state ³F₄, with an accuracy improved by factors of 110 and 50, respectively, compared to earlier measurements.