Isotope Effect on Adsorbed Quantum Phases: Diffusion of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="bold">H</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi mathvariant="bold">D</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>in Nanoporous Carbon

Quasielastic neutron scattering of ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ in the same nanoporous carbon at 10--40 K demonstrates extreme quantum sieving, with ${\mathrm{D}}_{2}$ diffusing up to 76 times faster. ${\mathrm{D}}_{2}$ also shows liquidlike diffusion while ${\mathrm{H}}_{2}$ exhibits Chudley-Elliott jump diffusion, evidence of their different relationships with the local lattice of adsorption sites due to quantum effects on intermolecular interactions. The onset of diffusion occurs at 22--25 K for ${\mathrm{H}}_{2}$ and 10--13 K for ${\mathrm{D}}_{2}$. At these temperatures, ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ have identical thermal de Broglie wavelengths that correlate with the dominant pore size.

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