N° 4. — Structure et mouvements moléculaires des hexafluorures de soufre, sélénium et tellure solides

Jean, Marcel; Drifford, M.; Rigny, Paul

doi:10.1051/jcp/1970670031

Cited by 60 publications

(33 citation statements)

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“…The approach to the problem was similar to that used by Miller and Gutowsky (14). The complete expression for motionally reduced second moments has been tabulated by Rigny et al (15). The value calculated in this manner is 1.45 G2 in agreement with a value of 1.26 GZ previously calculated for random in-plane rotation of the pyridinium ion (3).…”

Section: (A) Cw Nuclear Magnetic Resoizance Resultssupporting

confidence: 81%

Molecular motion, phase transitions, and disorder in the pyridinium halides

Ripmeester¹

1976

Can. J. Chem.

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JOHN A. RIPMEESTER. Can. J. Cnem. 54, 3453 (1976). The solid pyridinium chloride, bromide, and iodide salts were studied using 1H nuclear magnetic resonance and differential scanning calorimetry. Phase transitions were observed at 345 K for the chloride, 269 K for the bromide, and 247 K for the iodide. Well below each transition, the pyridinium ions are held rigidly in the crystal lattice, whereas above each transition the ions reorientate rapidly about an axis at right angles to the ring planes. From the temperature dependence of the spin-lattice relaxation times the high temperature phase reorientational activation energies were determined to be 1.55, 2.30, and 4.20 kcal/mol for the chloride, bromide, and iodide, respcctively. [Traduit par le journal]

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Section: (A) Cw Nuclear Magnetic Resoizance Resultssupporting

confidence: 81%

Molecular motion, phase transitions, and disorder in the pyridinium halides

Ripmeester¹

1976

Can. J. Chem.

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“…In all shells of all four monoclinic clusters studied the molecules in A sites had smaller rotational diffusion coefficients and rotational Lindemann indices, by perhaps 30%, than did those in B sites. On the other hand, there was little difference between molecules in the two sites with respect to their translational diffusion coefficients and Lindemann indices & Even though our primary criterion for rotational melting was based on the substantial increase in rotational freedom accompanying the transition to a disordered phase, our computations reveal a small but significant rotational diffusion in the ordered phase even at temperatures as low as 50 K. Although we are unaware of experimental measurements of molecular motions in monoclinic TeF 6, NMR studies of the orthorhombic phases of TeF 6 [32] and the very similar MoF 6 [33] (both of which have packing efficiencies nearly the same as those of the monoclinic phases [20]) show that the molecules continue to execute rotations well below the bccorthorhombic transition temperature.…”

Section: Discussionmentioning

confidence: 89%

Molecular dynamics study of orientational order and rotational melting in clusters of TeF6

Bartell

1994

Z Phys D - Atoms, Molecules and Clusters

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Abstract. Molecular dynamics simulations of the behavior of molecules in crystalline clusters of TeF 6 were carried out on systems of 100, 150, 250, and 350 molecules. Several diagnostic functions were applied to investigate whether rotational melting occurred before translational melting. These functions included the coefficient of rotational diffusion Do(T), the "orientational Lindemann index" ~o(T), the °' orientational angular distribution function" Q(O, T), and the "orientational pair-correlation function" go(r, T). All indicators implied that rotational melting occurred before translational melting, that it began with the outermost molecules, and that its onset for smaller clusters was at lower temperatures than for larger clusters. Results also showed that the rotational transition coincided with the transition from a lower symmetry phase (monoclinic) to cubic, a phenomenon that had been noted by others to occur with some regularity for systems of globular molecules.

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“…The existence of a phase transition at 96 K in solid SF6 was first observed in calorimetric measurements (3) and subsequently confirmed by nmr observations (4). From the temperature dependence of the nmr lineshape it was determined that the molecules were undergoing reorientational motion in the high temperature phase.…”

Section: Introductory Reviewmentioning

confidence: 82%

“…From the temperature dependence of the nmr lineshape it was determined that the molecules were undergoing reorientational motion in the high temperature phase. The crystal structure of this phase was shown by X-ray diffraction to be body-centred cubic (4). Later detailed nmr measurements (5) confirmed the reorientational motion of the high temperature phase, but also indicated a second phase transition at =45 K. The data showed that two inequivalent sites must exist in the low temperature phase and that reorientation of at least some molecules sets in between 45 K and the transition at 96 K. The conclusion from these studies was that the high temperature phase of SF6 was probably orientationally disordered, but the detailed nature of the disorder remained obscure.…”

Section: Introductory Reviewmentioning

confidence: 99%