Negative Ion of Boron: An Experimental Study of the 3 P Ground State
An investigation of the ${\mathrm{B}}^{\ensuremath{-}}({2p}^{2}{}^{3}{P}_{J})\ensuremath{\rightarrow}\mathrm{B}(2p{}^{2}{P}_{{J}^{\ensuremath{'}}})$ photodetachment thresholds using a tunable infrared laser source has yielded a substantially improved value for the electron affinity of boron and the first experimental data on the fine structure of the ionic ground state. The $J\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0\char21{}1$ and $J\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1\char21{}2$ splittings are found to be $3.23(15){\mathrm{cm}}^{\ensuremath{-}1}$ and $5.18(15){\mathrm{cm}}^{\ensuremath{-}1}$, respectively, and the electron affinity is determined to be $2256.12(20){\mathrm{cm}}^{\ensuremath{-}1}$ [(279.723(25) meV]. The present result for the electron affinity is the first to challenge the extensive and controversial theoretical studies of this system.