Observation of Molecular Motion in Solid<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>Below 4.2°K

NMR measurements in solid ${\mathrm{H}}_{2}$ at low ortho concentrations between 0.4 and 4.2\ifmmode^\circ\else\textdegree\fi{}K show that the equilibrium distribution of ortho molecules in the lattice is temperature dependent and is approached approximately exponentially in time at a given temperature. It is suggested that the rearrangement process occurs by means of ortho-para interchange.

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