Rotational diffusion in the rotator phase of n-alkanes

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Abstract
From quasielastic neutron scattering experiments performed in the rotator phase of n-alkanes (CnH2n+2), as a function of both n and temperature, two types of rotational diffusion have been detected. Type B corresponds to a uniform rotational diffusion, whereas type A corresponds to a hindered rotation, probably limited to large amplitude oscillations. It is the first time that type A rotational diffusion, given by the orthorhombic symmetry phase RI, is observed. On increasing the temperature it rapidly evolves towards the type B diffusion. Correlation times τ which seem to be rather independent of the phase type are of the order of 5×10−12 s.