Dynamic properties of dioctanoyl peroxide guest molecules constrained within the urea tunnel structure: A combined incoherent quasielastic neutron scattering and solid state 2H nuclear magnetic resonance investigation

Abstract

The dynamic properties of dioctanoyl peroxide guest molecules within the urea host tunnel structure in the dioctanoyl peroxide/urea inclusion compound have been investigated by incoherent quasielastic neutron scattering (IQNS) and solid state 2H nuclear magnetic resonance (NMR) techniques. The IQNS investigations were carried out on samples of urea inclusion compounds containing perdeuterated urea to ensure that the incoherent scattering is dominated by the dioctanoyl peroxide guest molecules. Using semioriented polycrystalline samples, translational motions of the guest molecules along the tunnel were investigated separately from reorientational motions of the guest molecules about the tunnel axis. The 2H NMR experiments used dioctanoyl peroxide deuterated selectively in both the α CD2 groups and urea with natural isotopic abundance. The dynamic models that have been found to describe the translational and reorientational motions of the guest molecules from the IQNS and 2H NMR data are discussed in detail. The reorientational dynamics of the guest molecules about the tunnel axis can be described by a model of uniaxial rotational diffusion in a twofold potential, and the translations of the guest molecules along the tunnels can be interpreted by a model of translational jumps between sites with unequal probabilities of occupation. These models differ markedly from those found previously to describe the dynamic properties of alkane guest molecules within the urea tunnel structure.