On Subthreshold Ionization of Helium Droplets, Ejection of He+, and the Role of Anions

Abstract

The mechanism of ionization of helium droplets has been investigated in numerous reports but one observation has not found a satisfactory explanation: How are $H{e}^{+}$ ions formed and ejected from undoped droplets at electron energies below the ionization threshold of the free atom? Does this path exist at all? A measurement of the ion yields of $H{e}^{+}$ and $H{e}_2^{+}$ as a function of electron energy, electron emission current, and droplet size reveals that metastable $H{e}^{\ast -}$ anions play a crucial role in the formation of free $H{e}^{+}$ at subthreshold energies. The proposed model is testable.

Cited by in corpus (1)

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