Measurement of the electron affinity of potassium

A high-resolution measurement of the electron affinity of potassium has been made using the laser photodetachment threshold technique. A sensitive collinear laser-negative-ion beam apparatus was used in the experiment. We investigated the threshold for photodetachment of K^- leading to the formation of residual K atoms in the 4p_3/2 state. These excited atoms were selectively detected by use of resonance ionization. The result, an electron affinity of 501.459(12) meV for K, is significantly more accurate than previous measurements and current theory.