Method for Studying Low Energy Ion‐Molecule Reactions Using Monoenergetic Ions

An experimental technique is described for the study of ion‐molecule reactions permitting the investigation of ions with kinetic energies in the range 0–3 eV which introduces negligible spread in ion energy. A 20 nsec ionizing pulse is used to produce ions in the reaction chamber to which a steady dc electric field is applied. Because of the short time interval for ionization all ions have essentially the same energy and move as a ``bunch'' under the influence of the applied field. Thus the energy of the ions at any subsequent time may be readily calculated, and the energy dependence of ion‐molecular interactions may be studied. Practical considerations, determined by source dimensions, limited the maximum energy to 1.3 eV in the present study for the reaction CH4++CH4 → CH5++CH3.