A remeasurement of the cross section for charge exchange in H+-H-collisions

Abstract

The cross section for the charge-exchange reaction H+ +H- -> H+H has been measured, using an inclined-beams technique, over an energy range from 025 to 10 kev (in the frame of reference in which the target H- ion is at rest). A proton beam collides with an H- beam at an intersection angle of 20° and hydrogen atoms formed from proton charge exchange in the above reaction are detected. This technique provides a relative collision energy much lower than the energy of either beam and ensures separation together with efficient detection of the reaction products in each beam after the collision. The measured cross section, which falls from about 21 × 10-14 cm2 at 025 kev to 25 × 10-15 cm2 at 10 kev, is compared with the theory derived by Bates and Lewis in 1955 and three points of discrepancy are identified. At high energies the calculated cross section decreases as E-1/2, whereas the experimental energy dependence is closer to E-1. The experimental cross section is between two and three times larger than the calculation and it shows structure in the region of 1 kev.