Infrared Photodetachment Spectroscopy of As$^{- }$

The binding energy and fine structure splittings of the arsenic negative ion (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 -- 0.81 eV. An $s$-wave threshold was observed near 0.8048 eV due to the opening of the As$^{-}$ (4$p^{4} \quad ^{3}P_{2})$ to As (4$p^{3} \quad ^{4}S_{3/2})$ ground state to ground state transition, which defines the electron affinity of As. Thresholds were also observed for detachment from the J = 0 and 1 levels of As$^{-}$, permitting accurate determination of the fine structure splittings. 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).