Atomic hydrogen and deuterium mixtures at 1 K

Abstract

It has been predicted that the spin exchange broadening cross section for collisions between atomic hydrogen and deuterium (H and D) is over 300 times as large as the corresponding value for H-H collisions at 1 Kelvin. By monitoring the broadening of the ΔF=1, Δm F =0 hyperfine transition of the H atom, we were able to infer the density of D atoms present in a mixture of H and D confined by superfluid liquid helium ( l- 4He) walls at temperatures between 1.0 and 1.2 K. Measurements have been made of the energy required to dissolve a D atom into l- 4He as well as the rate constants for the H-D- 4He and D-D- 4He gas phase recombination processes. The theoretical spin exchange broadening cross section has been indirectly confirmed.