Investigation of the production of singly charged ions in a rf quadrupole ion trap

A three-dimensional rf quadrupole ion trap has been constructed to study ion production by electron-impact ionization. Gases and atoms in an atomic beam can be investigated. The method can be extended to the study of photon ionization and of the production of multiply charged ions by a single collision and/or by step-by-step ionization. Total electron-impact ionization cross sections of helium have been measured and are sigma/sub e/(350 eV) =0.26(6) x 10-16 cm2 and sigma/sub e/(500 eV) =0.21(4) x 10-16 cm2. Equations are derived to operate the rf ion trap in the symmetric storage mode