Experimental Measurements of the Electron Affinity of Gallium and the Fine Structure of Ga$^{-}$

The electron affinity of gallium and the negative ion fine structure splittings of Ga$^{-}$ have been measured using tunable laser photodetachment threshold spectroscopy. The relative cross sections for neutral atom production were measured with a crossed laser-ion beam apparatus over the photon energy range 0.27 -- 0.41 eV. An $s$-wave threshold was observed due to the opening of the Ga$^{-}$ (4$p^{2} \quad^{3}P_{0})$ to Ga (4$p$ $^{2}P_{1/2})$ ground-state to ground-state transition, yielding a preliminary value for the Ga electron affinity. $s$-wave thresholds were also observed for detachment from the J $=$ 1 and J $=$ 2 excited levels of Ga$^{-}$, yielding preliminary values for the fine structure splittings. The present values are compared with previous experimental [1, 2] and theoretical results [3-5]. \\[4pt] [1] W. W. Williams \textit{et al}., J. Phys. B \textbf{31}, L341 (1998); \\[0pt] [2] T. Andersen \textit{et al.}, J. Phys. Chem. Ref. Data \textbf{28}, No. 6, 1511 (1999). \\[0pt] [3] D. Sundholm \textit{et al.}, J. Phys. B \textbf{32,} 5853 (1999).\\[0pt] [4] J. Li\textit{ et al.}, J. Phys. B \textbf{45} 16500 (2012).\\[0pt] [5] Z. Felfli, \textit{et al.}, J. Phys. B \textbf{45 }045201 (2012).