Mass Spectrometry of Ions in Glow Discharges. IV. Water Vapor

Ions from the negative glow and Faraday dark space of discharges in water vapor have been analyzed with a mass spectrometer. The ions observed are of the form H3O+·(H2O)n with n=0 to 5. It is shown that the observations are altered by the sampling process to an extent which depends on discharge conditions and is sometimes quite large. This effect may be important whenever loosely bound ions are sampled from a plasma. The sequence of hydration reactions is examined in an approximate manner and it is concluded that the bond strength decreases as successive water molecules add to H3O+, falling sharply beyond n=3. The rate constants for the first few stages of the hydration process appear to increase with the size of the reactant ion.