An experimental method for evaluating the H 2 and D 2 contamination levels in a HD bottle

Abstract

Studies of one- and two-electron processes in collisions with hydrogen molecules using the time-of-flight technique are simplified by using the heteronuclear HD isotope because the H + and D + fragments can be easily distinguished from each other. The difference in the time-of-flight of H + and D + enable the fragments to be measured in coincidence with each other. However, it is hard to determine the purity of the HD target, in particular the H 2 contamination, because the H 2 + molecular ions coincide with the D + fragments. A method is suggested to determine the purity of a HD target to a precision of a few percent. This method is based on measuring the yield of very slow (< 0.5 eV) H + and D + fragments of HD bombarded by fast protons ( E > 1 MeV). The H 2 contamination is then determined by subtracting the theoretically evaluated contribution of the ground-state dissociation of the HD + molecular ion from the measured sum of both H + and D + low-energy fragments.