Nuclear relaxation during the formation of H2 from spin-polarized hydrogen

Abstract

We report an NMR study of solid H2 formed by the recombination of doubly polarized atomic hydrogen at a temperature of 0.3 K. The molecules are formed in a highly excited ortho state with MI=-1, thermalize through collisions with the coated4 walls of the containment chamber, and form a solid. The solid is essentially pure ortho H2 in the fcc phase, as expected. However, the nuclear polarization is close to zero, in contrast to the value of -1 if there was no relaxation, and +0.034 if the spin temperature was in equilibrium with the surface of the cell. Possible mechanisms for depolarization are discussed, though no plausible explanation for the loss has yet been found. © 1993 The American Physical Society.