Electron affinity of arsenic and the fine structure of As- measured using infrared photodetachment threshold spectroscopy

The binding energy and fine-structure splittings of the arsenic negative ion (As^-) have been measured using infrared photodetachment threshold spectroscopy. The relative cross section for neutral atom production was measured with a crossed ion-beam-laser-beam apparatus over selected photon energy ranges between 630-810 meV. An s -wave threshold was observed due to the opening of the As^-(4p⁴P3₂) to As(4p³S4_3/2) ground-state to ground-state transition, which yields the electron affinity of As to be 804.8(2) meV. s -wave thresholds were also observed for detachment from the J=1 and J=0 excited levels of As^- , permitting accurate determination of the fine-structure splittings of 127.6(2) meV for P3₁-P3₂ and 164.3(10) meV for P3₀-P3₂ . The present values are consistent with previous measurements and substantially reduce the uncertainties.