Proton magnetic resonance line shape measurements in solid ethane

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Abstract
The proton magnetic resonance absorption line shape has been measured for solid ethane in the temperature range from 4 K to the melting point. The linewidth and second moment have been derived from the data. The existence of two solid phases has been confirmed; the solid–solid phase transition temperature was determined to be 89.72 ±0.05 K, and the melting point 90.37±0.05 K. The higher temperature solid phase is characterized by a narrow liquidlike resonance line indicating rapid diffusion. In the lower temperature solid phase the linewidth is much greater and it increases in two stages as the temperature is lowered to 4 K. The second moment of the line has been compared with the result of model calculations and the types of molecular motion inferred. Even at the lowest temperatures the observed second moment is much less than would be appropriate for a rigid lattice; this is interpreted in terms of tunneling of the molecules about their threefold symmetry axes.