Quantum free-rotor transitions of partially deuterated NH3 in a Hofmann clathrate

Abstract We have studied the effect of partial deuteration on the quantum free-rotation of NH 3 groups in a Hofmann clathrate Ni(NH 3 ) 2 Ni(CN) 4 ·2C 6 H 6 with 30, 50 and 70 at% D. Because the H-atoms are labile, statistical mixtures of NH 3 , NH 2 D, NHD 2 and ND 3 are obtained. To our surprise, the free-rotor peak of NH 3 is considerably more intense than expected on the basis of the calculated concentration. Further, for a given level of deuteration, the relative intensities of the free-rotor peaks due to NH 3 , NH 2 D, and NHD 2 vary with respect to one another as a function of temperature. We will present our results and discuss possible origins of this intriguing behaviour. Diffuse scattering experiments are proposed to obtain new information.