Merging Beams, A Different Approach to Collision Cross Section Measurements

A different approach has been developed to measure two‐body collision cross sections in the energy range from thermal to several hundred electron volts. Two molecular beams are merged and move in the same direction along a common axis. Ion‐neutral reactions are discussed but the techniques could also be used for ion‐ion and neutral‐neutral collisions. Advantages of the merging beams technique over conventional beam‐gas and crossed beam methods include accessibility (with good energy resolution) to the energy region from a few tenths of one to a few electron volts; the possibility of measuring cross sections for two general, labile species; and relative ease in collecting and detecting products for total reaction cross section measurements. The principles of the method and details of the instrument are discussed. A cross section for the resonant charge transfer of Ar was measured. Reasonable agreement with some previous measurements, and other tests, indicate that the basic principles of a merging beams technique are valid and that the apparatus performs satisfactorily.