¹H NMR Relaxation of Methanol CH₃OD up to High Pressures of 250 MPa and to 523 K

¹H NMR spin-lattice relaxation rates 1/T₁ of partly deuterated methanol CH₃OD were measured at six temperatures between 298 K and 523 K. At each temperature pressures between 1 MPa and 250 MPa were applied. An externally heated autoclave served as high pressure cell. At pressures above 100 MPa the isobars of the relaxation time T₁ have a positive temperature dependence in the whole temperature range, showing that ¹H-¹H dipole-dipole relaxation dominates, wheras at low pressures (≤100 MPa) and high temperatures a negative temperature dependence occurs, reflecting a dominating spin-rotation interaction, caused by a comparatively free rotation of the CH₃-group. Thus, the transition between the two different relaxation mechanisms and their dependence on pressure and temperature can be clearly observed. Up to about 423 K one could make a quantitative estimation of the spin-rotation relaxation contribution and it turned out that, at a given temperature, this relaxation contribution and thus the free rotation of the CH₃-group seems not to be appreciably influenced by the applied pressure. Finally, with density dependent isotherms a comparison with relaxation times in supercritical water is made.