Neutron scattering study of the methyl-group reorientations and the low temperature phase transition in (CH3)2 SnF2

Abstract

The reorientation of the methyl groups in solid (CH3)2SnF2 has been investigated by neutron quasielastic scattering. It is found that a phase transition occurs in the solid at about 70 K, which might be of second order. The shape of the measured quasielastic lines can be described by instantaneous threefold jumps of the methyl groups. From the derived residence times as a function of temperature below the phase transition, an activation energy Ea/kB=250 K and a residence time at infinite temperatures τ0=0.10 ps have been determined. Above the phase transition the activation energy is at least a factor 2 smaller.

Coupled pairs of quantum rotors in (CH3)2SnCl2: An inelastic neutron scattering study

“…The calculated values are shown as bars in the measured spectra (Figs. 2,3,8). The width of the tunnelling line at 40~teV (h(o)l-O)o) and the weak line at 0.5 geV (he%) are in as good agreement with the measured data as is the overall splitting (0.3 meV) of the first excited librational state.…”

“…At Tc=66_+5 K the crystal shows a phase transition. The low temperature structure is not known but the methyl groups experience only a shallow rotational potential [3,4] and are still equivalent [4]. It might be, that the low temperature phase differs from the high temperature structure only by the rotational ordering of the methyl groups.…”

An infrared and Raman study of the phase transitions in dimethyltin difluoride

“…The behaviour of dimethyltin difluoride at low temperatures has been studied by many techniques, including calorimetry, neutron scattering and Mossbauer, NMR and vibrational spectroscopies. [1][2][3][4][5][6][7] Under ambient conditions, the compound adopts a tetragonal layer structure, space group 14/rnrnrn(D4,),8 2 = 2, with a = 4.24 and c = 14.16 A (Fig. 1).…”