Accurate Electron Affinity of Iron and Fine Structures of Negative Iron ions

Ionization potential (IP) is defined as the amount of energy required to remove the most loosely bound electron of an atom, while electron affinity (EA) is defined as the amount of energy released when an electron is attached to a neutral atom. Both IP and EA are critical for understanding chemical properties of an element. In contrast to accurate IPs and structures of neutral atoms, EAs and structures of negative ions are relatively unexplored, especially for the transition metal anions. Here, we report the accurate EA value of Fe and fine structures of Fe(−) using the slow electron velocity imaging method. These measurements yield a very accurate EA value of Fe, 1235.93(28) cm(−1) or 153.236(34) meV. The fine structures of Fe(−) were also successfully resolved. The present work provides a reliable benchmark for theoretical calculations, and also paves the way for improving the EA measurements of other transition metal atoms to the sub cm(−1) accuracy.