On Subthreshold Ionization of Helium Droplets, Ejection of He+, and the Role of Anions
The mechanism of ionization of helium droplets has been investigated in numerous reports but one observation has not found a satisfactory explanation: How are He+ 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 He+ and He2+ as a function of electron energy, electron emission current, and droplet size reveals that metastable He*− anions play a crucial role in the formation of free He+ at subthreshold energies. The proposed model is testable.
Physical Chemistry Chemical Physics
Royal Society of Chemistry
Digital Object Identifier (DOI)
M. Renzler, M. Daxner, N. Weinberger, S. Denifl, P. Scheier, and O. Echt, On Subthreshold Ionization of Helium Droplets, Ejection of He+, and the Role of Anions Phys.Chem.Chem.Phys.16 (2014) 22466-22470, Communication, DOI: 10.1039/C4CP03236E, Sep 2014.