A Proton Magnetic Resonance and Gravimetric Study of Water and Isopropanol Adsorption on Microcrystalline Rutile. III. Adsorption of Isopropanol

The proton spin‐lattice (T1) and spin‐spin (T2) relaxation times of isopropanol (CH3)2CDOD chemisorbed on two types of preconditioned rutile surfaces (free of water and covered with chemisorbed D2O) were measured as function of temperature (100 to 300 K) and resonance frequency (20 to 90 MHz). The spin‐lattice relaxation rates were found to be separable according to 1/T1 = 1/T1D + 1/T1S. The proton dipolar term 1/T1D as well as T2 turned out to be essentially independent on the preloading with water indicating the same surface sites to be involved in alcohol chemisorption for both types of preconditioned surfaces. The temperature independent term 1/T1S was found to be proportional to the inverse of the square root of the resonance frequency signifying proton relaxation via spin diffusion at paramagnetic centers to be operative. – From T1D the methyl group reorientation rate was evaluated as 1/τ = 2·1011 exp(– 1100/T K−1) s−1. The absolute values of T1D could not be accounted for quantitatively on the basis of known models of dipolar spin relaxation of protons contained in rotating methyl groups.