Electron-spin resonance of atomic hydrogen and deuterium at low temperatures

The electron-spin resonance at 9 GHz of a gas of hydrogen and deuterium has been studied at low temperatures. At 4 K the observation of both H and D provides a rough estimate of the adsorption energy of D on solid ${\mathrm{D}}_2$ of 55 K. Below 1 K the ESR of H was used to study electronic spin relaxation, which was due primarily to impurities on the walls of the cavity. This impurity relaxation precluded the possibility of observing a nonthermal population distribution among the states of the atom calculated to occur in its absence. No ESR signal from D was detected below 1 K although a flux into the low-temperature cell was measured. If the recombination is assumed to occur on the surface to which D is bound by 2.6 K, the limit on the density implies that the cross-length for surface recombination is very large, on the order of 300 Å. Such a large cross-length would suggest that a pair of D atoms may form a weakly bound two-dimensional dimer on the surface.