PHOCKRDlNCiS OF THK XI ni MKKTINCi OF THF INTEHNVriONAI , S ( K ' IKT \ OF MAGNETIC

We report on the variation of a methyl tunnel splitting with pressure. The measurements are the first studies of thepressure variation of a methyl tunnel splitting using low-field, of order 80 gauss, dipole-dipole driven NMR spectroscopywith rapid field-cycling. Pressures up to 1.8kbar were applied with an operating temperature of 4.2K. In addition protonspin-lattice relaxation time Ti data has been collected up to 6.25kbar. Using an established theoretical model the twodata sets have been combined to give the tunnel splitting throughout the entire pressure range. Further calculations givethe potential barriers, including a small six fold term, needed within the crystal to produce these results. The overallheight of the hindering potential and its shape are compared with the potential calculated from the crystal structure.