The Positive Ray Analysis of Water Vapor Ionized by Impact of Slow Electrons

An electromagnetic method of separating gas ions of different mass, such as that used by Dempster, has been employed in a study of the ions produced by electron impact in water vapor. The principal ions appearing were (H₂O)⁺ and (OH)⁺. Of these the (H₂O)⁺ ions were more abundant. Unmistakable evidence was obtained that a third type of ion, probably (H₃O)⁺, was produced in very small quantities. H⁺ and H₂⁺ ions were always very few in number or unobservable. No (OH)^- or any other negative ions were observed.Ionization potentials for (H₂O)⁺ and (OH)⁺.---The ionization potential corresponding to (H₂O)⁺ was 13±{}1.5 volts, being probably in agreement with the ordinarily measured ionization potential. The (OH)⁺ ionization potential was not distinguishably different, but it was difficult to measure this quantity owing to some overlapping of the (H₂O)⁺ and (OH)⁺ peaks.Relative abundance of the ions as a function of pressure.---A study was made of variation in the relative abundance of the ions as a function of pressure. The (H₂O)⁺ ion appears to be the primary ion, as it predominates at low pressures, but is of the same order of magnitude as the (OH)⁺ ion at high pressures (0.007 mm).