Inelastic neutron scattering study of the proton dynamics in HNO3 graphite intercalation compounds

Inelastic neutron scattering (INS) spectra of the alpha-form third stage of the graphite-nitric-acid intercalation compound G-HNO3 (C15HNO3) at 20 K are presented for a powder sample and for aligned platelets of highly ordered pyrolytic graphite (HOPG-HNO3), with momentum transfer direction either parallel or perpendicular to the layer planes. The dynamics of the NO3 entities are amenable to a slightly non-planar structure and tunnel splitting due to inversion is tentatively assigned at 100 cm(-1). The NO3 mean-plane is tilted 35 +/- 5 degrees to the graphite layer. Proton dynamics are twofold. Bound protons form strong hydrogen bonds, canted at similar to 45 degrees with respect to the layers, between NO3 entities. In addition, a continuum of intensity is assigned to recoil of free protons. (C) 1999 Elsevier Science B.V. All rights reserved.