There are also difficulties in interpreting the T1 relaxation data, Figure . Although the temperature dependences can be fitted to Arrhenius behavior, it is not obvious that the parameters obtained relate to molecular behaviour. For example, the activation energy for the acetone motion of 7.9 ± 0.2 kJ mol -1 derived from Arrhenius-type analysis is small, and would be expected to correspond to a fast motion, while the sign of the slope implies that the motion is still slow compared the 2 H Larmor frequency (10s MHz). This inability to reconcile models of the lineshape and relaxation data taken in isolation was illustrated schematically in Figure .