Rotational tunneling of ammonia in (NH_3)K_3C_(60)

摘要

The rotational dynamics of NH_3 in the ammoniated fulleride (NH_3)K_3C_(60) are studied by the inelastic neutron scattering technique. Well-defined excitations appear in the low-energy spectra at 1.5 K as a broad band centered at approx 350 #mu#eV with shoulders at approx 240 and 590 #mu#eV. The temperature dependence of their intensities, energies, and widths is consistent with their assignment to rotational tunneling transitions of the NH_3 molecule. The estimated barrier of the threefold hindrance potential to rotation of the H atoms about the K-N axis is approx 5.7 meV. The existence of minority hindering sites with both larger (approx 8 meV) and smaller (approx 2 meV) torsional barriers shows that orientational disorder effects survive in (NH_3)K_3C_(60) even at low temperatures.