Purely Spatial Quantum Diffusion of H Atoms in Solid H2 at Temperatures below 1 K

Abstract

We report on a direct measurement of the quantum diffusion of H atoms in solid molecular hydrogen films at T ¼ 0.7 K. We obtained a rate of pure spatial diffusion of H atoms in the H 2 films, D d ¼ 5ð2Þ × 10 −17 cm 2 s −1 , which was 2 orders of magnitude faster than that obtained from H atom recombination, the quantity used in all previous work to characterize the mobility of H atoms in solid H 2 . We also observed that the H-atom diffusion was significantly enhanced by injection of phonons. Our results provide the first measurement of the pure spatial diffusion rate for H atoms in solid H 2 , the only solid state system beside 3 He − 4 He mixtures, where atomic diffusion does not vanish even at temperatures below 1 K.