An experimental study of charge transfer in proton-atomic hydrogen collisions at impact energies above 40 keV

The crossed beam technique has been used to study charge transfer in proton-atomic hydrogen collisions between 40 and 130 keV. A proton beam from a Van de Graaff accelerator was arranged to intersect a modulated beam of atomic hydrogen derived from a furnace source. The flux of fast neutral atoms produced by charge transfer in the beam intersection region was measured by a method based on double electrostatic deflexion of the proton beam. The ratio of the charge transfer cross section Q1 in atomic hydrogen to that in molecular hydrogen Q2 was determined by comparing the signals when the beam from the furnace was mainly atomic and when the beam was entirely molecular. Above 50 keV, measured ratios Q1 / Q2 were consistently less than ½. Absolute values of Q1, which represent total cross sections for capture into all states of atomic hydrogen, were obtained by reference to known values of Q2. Above 50 keV, the results agree fairly well with theoretical values due to Jackson & Schiff. When considered in conjunction with the low energy data of Fite and his collaborators, the results suggest that capture into excited states in the range 20 to 50 keV occurs to a greater extent than that predicted by Jackson & Schiff.