Inelastic neutron scattering study of the proton dynamics in HNO3 graphiteintercalation 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 a re presented for a powder sample and for aligned platelets of highly ordere d pyrolytic graphite (HOPG-HNO3), with momentum transfer direction either p arallel or perpendicular to the layer planes. The dynamics of the NO3 entit ies are amenable to a slightly non-planar structure and tunnel splitting du e 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 Scie nce B.V. All rights reserved.