M. Prager, P. Schiebel¹, J. Combet^2
1University of Tübingen, Tübingen, Germany
²Institut Laue-Langevin, Grenoble, France

P-iodotoluene shows head-to-tail disorder. Methyl tunnelling rotation is used to study this disorder which manifests itself by the presence of two broad tunnelling transitions. Their relative intensities represent an order parameter. Average potential strengths and widths of gaussian potential distributions are derived. The potential shape is further refined by including methyllibrations.