Fig. 4.

Magic-angle-spinning proton NMR spectra of H₂O @ C₆₀, taken in a magnetic field of 14.1T (proton precession frequency ≈-600.0 MHz). All spectra were obtained by taking the Fourier transform of a single transient after a 90° excitation pulse and subjecting it to Lorentzian linebroadening with a linewidth of 200 Hz followed by baseline correction. The sample temperatures and spinning frequencies are (A) 22.8 K, 8.86 kHz; (B) 18.5 K, 8.38 kHz; (C) 13.0 K, 7.12 kHz; (D) 9.6 K, 5.04 kHz. The peaks indicated by asterisks are spinning sidebands. The grey line is a simulation for randomly oriented pairs of protons with a magnetic dipole–dipole interaction of -5.5 kHz.