Published online by Cambridge University Press: 10 February 2011
23Na and 1H NMR studies have been carried out for a NaxHyC60 superconductor The peak position of the 23Na NMR spectrum exhibits discontinuous upfield shift of 30 ppm at about 250 K, indicates a first order phase transition From the line shape of the 23Na spectrum obtained at 7 K, the quadrupole coupling constant tensor is evaluated to be |e2Qq/h|=3.7 MHz with the asymmetry parameter η = 0.95. The 1H NMR spectrum suggests an anionic hydrogen state with weakly delocalized nature.