An N.M.R. study of an n-butane film on graphite

Abstract

The proton spin-lattice (1/T ₁) and spin-spin (1/T ₂) relaxation rates of various n-butane isotopes ((CD₃)₂(CH₂)₂, (CH₃)₂(CD₂)₂, C₄H₁₀, C₄D₁₀ (2 per cent H), a mixture of C₄H₁₀ and C₄D₁₀) adsorbed on the graphitized carbon black Graphon were measured as function of temperature (293 to 130 K) at the resonance frequencies 21·7, 59·4 and 89·1 MHz. The relaxation rates obtained were separated into contributions due to intramolecular proton dipolar, proton-electron dipolar as well as magnetic shielding anisotropy couplings. The analysis of the data was accomplished on the basis of models which take into account various anisotropic rotational motions and surface diffusion of the adsorbed molecules as well as the diamagnetic and paramagnetic properties of the support material. The correlation times of the anisotropic molecular rotations are in agreement with the results of a previous deuteron N.M.R. study. The surface diffusion coefficients of the adsorbed molecules were derived from the exclusively orientational dependent spin hamiltonians (intramolecular dipolar and shielding anisotropy) and compare well with data from macroscopic surface flow measurements.