Measurement of the Electron Affinity of Thallium by Photodetachment Threshold Spectroscopy*

The electron affinity of thallium has been measured using tunable laser photodetachment threshold spectroscopy. The relative cross section for neutral atom production following photodetachment from Tl$^{-}$ was measured with a crossed laser--ion beam apparatus over the photon energy range 0.30 -- 0.50 eV. An \textit{s}-wave threshold was observed due to the opening of the Tl$^{-}$ (6\textit{p}$^{2}$ $^{3}$\textit{P}$_{0}$) to Tl (6\textit{p} $^{2}$\textit{P}$_{1/2}$) ground-state to ground-state transition, yielding a preliminary value for the electron affinity of thallium. The electron affinity measured in the present work is compared with previous experimental [1] and theoretical [2] results. \\[4pt] [1] D. L. Carpenter, A. M. Covington, and J. S. Thompson, \textit{Phys. Rev. A} \textbf{61}, 042501 (2000); [2] see for example J. Li, Z. Zhao, M. Andersson, X. Zhang, and C. Chen, \textit{J. Phys. B-At. Mol. Opt. Phys.} \textbf{45}, 165004 (2012).