Near-threshold photodetachment of the Li- ion.

Abstract

The method of threshold-photodetachment spectroscopy has been used to measure the electron affinity of Li. Changes in the partial cross sections for the resolved h\ensuremath{\nu}+${\mathrm{Li}}^{\mathrm{\ensuremath{-}}}$(2 $^{1}$S)\ensuremath{\rightarrow}Li(2 $^{2}$S)+${\mathit{e}}^{\mathrm{\ensuremath{-}}}$(\ensuremath{\epsilon}p) ${(}^{2}$S\ensuremath{\epsilon}p) and h\ensuremath{\nu}+${\mathrm{Li}}^{\mathrm{\ensuremath{-}}}$(2 $^{1}$S)\ensuremath{\rightarrow}Li(2 $^{2}$P)+${\mathit{e}}^{\mathrm{\ensuremath{-}}}$(\ensuremath{\epsilon}s) ${(}^{2}$P\ensuremath{\epsilon}s) channels were separately investigated in the vicinity of the 2 $^{2}$P threshold. The near-threshold data in the $^{2}$P\ensuremath{\epsilon}s channel were fitted to a Wigner law to determine a threshold photon energy of 19 884.8\ifmmode\pm\else\textpm\fi{}1.6 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. An electron affinity of 4980.9\ifmmode\pm\else\textpm\fi{}1.6 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (617.6\ifmmode\pm\else\textpm\fi{}0.2 meV) is obtained upon subtraction of the well-known 2 $^{2}$P excitation energy. The position of the Wigner cusp in the $^{2}$S\ensuremath{\epsilon}p channel was measured to be 19 882.4\ifmmode\pm\else\textpm\fi{}4.0 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, in agreement with the more precise $^{2}$P\ensuremath{\epsilon}s-channel threshold energy.