Helium anion formation inside helium droplets*
Institut für Ionenphysik und Angewandte Physik, Universität
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Received in final form: 20 May 2016
Published online: 5 July 2016
The formation of He∗− is examined with improved electron energy resolution of about 100 meV utilizing a hemispherical electron monochromator. The work presented provides a precise determination of the three previously determined resonance peak positions that significantly contribute to the formation of He∗− inside helium nanodroplets in the energy range from 20 eV to 29.5 eV. In addition, a new feature is identified located at 27.69 ± 0.18 eV that we assign to the presence of O2 as a dopant inside the droplet. With increasing droplet size a small blue shift of the resonance positions is observed. Also for the relatively low electron currents used in the present study (i.e., 15–70 nA) a quadratic dependence of the He∗− ion yield on the electron current is observed.
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