Improvement of the merged-beam method and its application to the study of the reaction: H-+He+->H+He

It is shown that two parallel ion beams react at a rate that is independent of their density profiles when made to oscillate against each other in a two-dimensional scanning motion. An experimental set-up that makes use of this principle is described. Absolute cross sections obtained in this way are in good agreement with those obtained with the beams merging in the usual (static) mode. Cross sections for single-charge transfer between H-(D-) and He+ in the energy range 5-4000 eV are presented and compared to other existing data