Measurement of the Electron Affinity of Arsenic and the Fine Structure of As$^{- }$

The electron affinity of arsenic and the negative ion fine structure splittings of As$^{-}$ have been measured using tunable laser photodetachment threshold spectroscopy. The relative cross section for neutral atom production was measured with a crossed laser-ion beam apparatus over selected photon energy ranges between 0.63 -- 0.82 eV. An $s$-wave threshold was observed due to the opening of the As$^{-}$ (4$p^{4}$ $^{3}P_{2})$ to As (4$p^{3} \quad ^{4}S_{3/2})$ ground state to ground state transition, yielding a preliminary value for the As electron affinity of 0.80481(13) eV. $s$-wave thresholds were also observed for detachment from the J = 0 and J = 1 excited levels of As$^{-}$, yielding preliminary values for the fine structure splittings of 0.1276(2) eV for $^{3}P_{1}$ -- $^{3}P_{2}$ and 0.1643(6) eV for $^{3}P_{0}$ -- $^{3}P_{2}$. The values measured in the present work are consistent with previous measurements [1,2] and substantially reduce the uncertainties. [1] T.P. Lippa \textit{et al}., J. Chem. Phys. \textbf{109}, 10727 (1998); [2] G. Haeffler \textit{et al.}, Z. Phys. D \textbf{42}, 263 (1997).