N.M.R. studies of neopentane absorbed upon titanium dioxide

N.M.R. studies of neopentane adsorbed upon titanium dioxide between 80 K and 300 K for coverages between 0·5 and 2 monolayers show three different phases as a function of temperature. Above 200 K the adsorbed neopentane exists as a liquid, and rotational and translational diffusion coefficients have been determined by 13C relaxation times and the magnetic field gradient spin echo method respectively. Above 130 K the neopentane exists in a rotationally mobile solid phase in which rotation about axes both perpendicular and parallel to the surface occurs. On cooling below 130 K there is a gradual transition to a solid in which rotation is permitted only about an axis perpendicular to the surface. In the low temperature solid phase the inter- and intramolecular contributions to the linewidths have been separated using mixtures of neopentane and fully deuterated neopentane. Both these and the rotational diffusion coefficients in the liquid show the neopentane to be oriented with respect to the surface as a tripod.