Search for Fractionally Charged Ions in Helium Gas

A Van de Graaff accelerator facility has been used as a supersensitive mass spectrograph in a search for free $+\frac{1}{3}\mathrm{}\left|e\right|\mathrm{}$ and $+\frac{2}{3}\mathrm{}\left|e\right|\mathrm{}$ charged ions in helium gas. No such ions were found at a level of sensitivity better than 1 part in 3.9× ${10}^{14}$ He atoms. The mass ranges spanned were 0.13 to 7.5 amu for $+\frac{1}{3}\mathrm{}\left|e\right|\mathrm{}$ ions and 0.27 to 15.0 amu for $+\frac{2}{3}\mathrm{}\left|e\right|\mathrm{}$ ions.