Lovell, A; Fernandez-Alonso, F; Skipper, NT; Refson, K; Bennington, SM; Parker, SF; (2008) Quantum delocalization of molecular hydrogen in alkali-graphite intercalates. PHYS REV LETT , 101 (12) , Article 126101. 10.1103/PhysRevLett.101.126101.

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Abstract

The adsorption of molecular hydrogen (H-2) in the graphite intercalation compound KC24 is studied both experimentally and theoretically. High-resolution inelastic neutron data show spectral features consistent with a strong pinning of H-2 along a single axis. First-principles calculations provide novel insight into the nature of H-2 binding in intercalates but fail to account for the symmetry of the H-2 orientational potential deduced from experiment. The above discrepancy disappears once the H-2 center of mass is allowed to delocalize in the quantum-mechanical sense across three vicinal adsorption sites, naturally leading to the well-known saturation coverage of similar to 2H(2) per metal atom in this material. Our results demonstrate that H-2 storage in metal-doped carbon substrates can be severely affected by hitherto unexplored quantum-mechanical effects.

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