NMR lineshapes and scalar relaxation of the 17O-labelled water-endofullerene H2O@C60

The 17O isotopomer of the water-endofullerene H2O@C60 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 17O 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 17O nuclei. The data are consistent with rotational diffusion of the water molecule on the sub-picosecond timescale.