Photodetachment study of the1s3s4s4Sresonance in He−

Abstract

A Feshbach resonance associated with the ${1s3s4s}^{4}S$ state of He${}^{\ensuremath{-}}$ has been observed in the He${(1s2s}^{3}S)$ + ${e}^{\ensuremath{-}}(\ensuremath{\epsilon}s)$ partial photodetachment cross section. The residual He${(1s2s}^{3}S)$ atoms were resonantly ionized and the resulting He${}^{+}$ ions were detected in the presence of a small background. A collinear laser-ion beam apparatus was used to attain both high resolution and sensitivity. We measured a resonance energy ${E}_{\mathrm{r}}=2.959255(7)$ eV and a width $\ensuremath{\Gamma}=0.19(3)$ meV, in agreement with a recent calculation.