Integral cross sections for ion—molecule reactions. I. The guided beam technique

A technique is described, that allows the measurement of integral cross sections for ion-molecule reactions and electron-transfer processes in the energy range from typically 0.1 to 20 eV (lab). Basically similar to the tandem mass spectrometer method, it uses inhomogeneous oscillatory electric fields for the storage and guidance of the primary ions and for the collection of the secondary ions. By these means a reduction of the number of excited ions in the primary beam and a good definition of the kinetic energy are obtained, together with a collection and detection probability for the secondary ions, that approaches unity for all scattering angles in a broad energy band. Tire ion beam intensity (10⁵ to 10⁷ ions per second) is only weakly dependent on the kinetic energy down to typically 0.15 eV (lab). The distribution of the collision energies is mainly determined by the thermal motion of the reactant gas in the scattering chamber (T ≈ 300 K). Measurements are reported for the reactions Ar⁺ + D₂ → ArD⁺ + D and Ne⁺ + CO → C⁺ Ne+O.