A Tl and Tl(p) Study of Molecular Motion and PHASE Transitions in the Tetramethylammonium Halides.

摘要

The temperature dependences of methyl group and (CH4)4N(+) ion reorientations in the tetramethylammonium salts ((CH3)4N(+)X(-) with X =Cl,Br,I) were studied by means of the proton spin-lattice relaxation times in the static and rotating frame (T(1) and R(1rho)). The T(1) values calculated for the motions are in good agreement with the double minima observed for each compound. Activation energies and frequency factors were obtained for both motions from the temperature dependence of T(1) in the three salts. Rotating frame spin-lattice relaxation times were also measured over temperatures from 200to 380K for (CH3)4NCl,giving results in agreement with those for T(1). A discontinuity in the T(1) of (CH3)4NCl was found near 418K. This led us to make a preliminary DTA investigation with results indicating that a first-order phase transition may occur near 434K and another definitely at 521+1K. (Author)