The dynamic structure of acenaphthalene in the solid state: pulse nuclear magnetic resonance measurements

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Pulse nmr has been used to determine the temperature dependence of T1 at 9.2, 18, and 60 MHz and also T1ρ at 9.2 MHz and T1D at 18 MHz, for the proton resonance of solid acenaphthalene. The data indicate a discontinuity at ~130 K, coincident with the main thermal anomaly in the specific heat curve, and suggest the occurrence of two distinct molecular motions with activation energies 14.2 kJ mol−1 and 18.9 kJ mol−1. Calculations using non-bonded atom–atom potential functions explain qualitatively the results of the nmr study and it is suggested that the two motional processes may be due to two sets of crystallographically different acenaphthalene molecules.