Unexpected high energy ions from a chemical ionization source

Doubly charged rare gas cations are produced in a chemical ionization source under conditions in which the energy of the primary ionizing electrons is more than 20 eV below the energetic threshold. The formation mechanism consists of creating secondary electrons outside the ion source followed by the acceleration of some of these electrons into the source where they initiate high energy ionization processes. Evidence suggesting that the secondary electrons arise from ionizing collisions between accelerated ions and background gas is presented. This process is expected to occur generally when positive ion chemical ionization is performed in magnetic deflection instruments