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

Inelastic neutron scattering (INS) spectra of the α-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° to the graphite layer. Proton dynamics are twofold. Bound protons form strong hydrogen bonds, canted at ∼45° with respect to the layers, between NO3 entities. In addition, a continuum of intensity is assigned to recoil of free protons.