Measurement 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$p^{2} {}^{3}P_{\mathrm{0}}$) 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 values measured in the present work are compared with previous results [1, 2].\\[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).