Dynamics of Krypton Atoms in Clathrate by the Mössbauer Technique

The temperature dependence of the mean-square displacement 〈x2〉 of the Kr guest atoms in the hydroquinone–Kr clathrates has been studied by the Mössbauer effect. The results show that at all temperatures the observed 〈x2〉 is about twice as large as can be accounted for by the “rattling” frequency observed in the far infrared. This implies that low lattice frequencies contribute substantially to the motion of the Kr atoms and therefore the system cannot be described solely in terms of the van der Waals “particle-in-a-box” model.