Charge stripping reactions of ions formed from methane,ammonia, water and hydrogen sulphide by protonation and by electron impact

The minimum energy, Q_min, necessary to convert an ion m₁⁺ to a doubly charged ion m₁²⁺ is obtained for 19 different ions from methane, ammonia, water and hydrogen sulphide by charge stripping using nitrogen collision gas. The ions studied include the MH]⁺ ions formed by chemical ionization in a high pressure source. Stable m₁²⁺ ions could not be formed in the case of NH₄]⁺, NH]^+˙, H₂O]^+˙ and OH]⁺. Even in these cases the value of Q_min could be estimated by studying the fragments formed from the unstable m₂₊ ions. In several cases, the energy required to form m₁²⁺ ions is less than the literature value for the ionization energy of m₁⁺. This is discussed in terms of the possibility of the presence of excited states of m₁⁺ in the present experiments.