Atomic hydrogen-deuterium mixtures at 1 kelvin: Recombination rates,spin-exchange cross sections,and solvation energies

A new technique has been applied to the study of atomic hydrogen and deuterium mixtures confined by liquid helium coated walls. The method uses standard low-field hyperfine magnetic resonance of the H atoms at 1420 MHz, but takes advantage of the dramatically different spin-exchange broadening for H-H and H-D collisions to simultaneously monitor the H and D densities. This provides a powerful means for studying the interaction of D with itself and with liquid helium, something otherwise difficult to achieve, and it also makes possible the study of spin-exchange and recombination interactions between H and D. A wide range of experimental results are presented, including the rate constants for H-D and D-D recombination, the spin-exchange broadening cross sections for H-D and D-D collisions, the H-D spin-exchange frequency shift cross section and an improved value for the H-⁴He buffer gas shift. Finally, a detailed study of the solvation of D into liquid⁴He has yielded an improved value for the salvation energy, a useful lower bound for the effective mass for D in liquid⁴He, and evidence for the reaction D + HD D₂ + H on the surface under the liquid⁴He film.