Merged electron-ion beam experiments. I. Method and measurements of (e-H₂⁺) and (e-H₃⁺) dissociative-recombination cross sections

A merged-beam experiment designed to study collisions between electrons and molecular ions at very low energies and with high energy resolution is described. The theory behind the technique is reviewed and a comparison is made with other intersecting-beam techniques. Cross sections for dissociative recombination of H2+ and H3+ with electrons have been measured through the energy range 0.01-4 eV with an estimated energy resolution of approximately 0.04 eV. The structure found in both curves reflects the formation of Rydberg states of the molecules which in some cases choose to decay through the autoionisation and pair-production channels.