Pressure dependence of the rotational ground state tunnel splitting in Ni(NH 3) 6I 2

Abstract

Inelastic neutron scattering techniques have been used to determine the rotational tunnel splitting of the librational ground state of ammonia molecules in Ni(NH 3) 6I 2 as a function of hydrostatic pressure up to 5.6 kbar at 8 K. The resulting exponential dependence of the tunnel splitting on pressure was interpreted with the help of a concurrent measurement of the compressibility to suggest a dependence on the interatomic distance as r −9 of the orientational potential. The phase transition temperature at 5.6 kbar was determined to be 27 K compared with 19.9 K at atmospheric pressure.