NMR Lineshapes and Scalar Relaxation of the Water-Endofullerene H O@C.

The O isotopomer of the water-endofullerene H O@C displays a remarkable proton NMR spectrum, with six well resolved peaks. These peaks are due to the J-coupling between the water protons and the O nucleus, which has spin-5/2. The resolution of these peaks is enabled by the suppression of water proton exchange by the fullerene cage. The six peaks display an unusual pattern of linewidths, which we model by a Liouville-space treatment of scalar relaxation due to quadrupolar relaxation of the O nuclei. The data are consistent with rotational diffusion of the water molecules on the sub-picosecond timescale.