Abstract
We present an experimental determination of the electron-impact ionization cross section of the $1s2s\phantom{\rule{0.16em}{0ex}}^{3}S$ state of helium, for which there is a serious long-lasting discrepancy between theory and experiment. A technique for the production of a fast, intense beam of helium in the $1s2s\phantom{\rule{0.16em}{0ex}}^{3}S$ state only has been developed for this purpose, based on photodetachment of the ${\mathrm{He}}^{\ensuremath{-}}$ anion. The cross section is measured using the animated crossed beam technique. The present results are much lower than the experimental data of Dixon et al. [J. Phys. B 9, 2617 (1976)] and are in excellent agreement with the calculation of Fursa and Bray [J. Phys. B 36, 1663 (2003)].
Published Version
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