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Questionable negative Ion formation process
I deleted the section about the negative ion formation process because the mechanism will not work as proposed in the article (M* + surface ---> M+ + surface + e-). If in this case the He metastable (denoted as M) has an energy of 19.8 eV. The ionization potential of He is 25 eV. Thus in order to get the excited He into an ionized state(denoted as M+) you would have to let it collide with the surface with at least 5.2 eV....this is under these conditions not possible!
