NUCLEAR SPIN-LATTICE RELAXATION AND EVIDENCE FOR A LOW TEMPERATURE PHASE TRANSITION IN SOLID n-D2

1978 ◽  
Vol 39 (C6) ◽  
pp. C6-92-C6-94 ◽  
Author(s):  
N. S. Sullivan ◽  
M. Devoret
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Nuclear Spin ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
Nuclear Spin Lattice Relaxation ◽  
Temperature Phase Transition ◽  
Low Temperature Phase

Phase transitions in solid cycloheptene

1990 ◽  
Vol 68 (4) ◽  
pp. 604-611 ◽  
Author(s):  
Julian Haines ◽  
D. F. R. Gilson
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
Low Temperature Phase

The phase transition behaviour of cycloheptene has been investigated by differential scanning calorimetry, proton spin-lattice relaxation, and vibrational spectroscopy (infrared and Raman). Two solid–solid phase transitions were observed, at 154 and 210 K, with transition enthalpies and entropies of 5.28 and 0.71 kJ mol−1 and 34.3 and 3.4 JK−1, respectively. Cycloheptene melted at 217 K with an entropy of melting of 4.5 JK−1 mol−1. The bands in the vibrational spectra of the two high temperature phases were broad and featureless, characteristic of highly disordered phases. The presence of other conformers, in addition to the chair form, was indicated from bands in the spectra. The ring inversion mode was highly phase dependent and exhibited soft mode type behaviour prior to the transition from the low temperature phase. The low frequency Raman spectra (external modes) of these phases indicated that the molecules are undergoing isotropic reorientation. In the low temperature phase, the vibrational bands were narrow; the splitting of the fundamentals into two components and the presence of nine external modes are consistent with unit cell symmetry of either C2 or Cs with two molecules per primitive unit cell. A glassy state can be produced from the intermediate phase and the vibrational spectra were very similar to those of the high temperature phases, indicating that static disorder was present. The barriers to reorientation, as obtained from proton spin-lattice relaxation measurements, are 9.0 kJ mol−1 in both the high temperature phases, and 15.4 kJ mol−1 in the low temperature, ordered phase. Keywords: cycloheptene, phase transition, differential scanning calorimetry, NMR, vibrational spectroscopy.

Deuterium NMR Study of the Solid-Solid Phase Transition in Phenethylammonium Bromide

1991 ◽  
Vol 46 (8) ◽  
pp. 691-696 ◽  
Author(s):  
Marco L. H. Gruwel ◽  
Roderick E. Wasylishen
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Line Shape ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
H Nmr ◽  
Line Shapes ◽  
Low Temperature Phase

AbstractUsing 2H NMR, the dynamics of the cation in phenethylammonium bromide were studied in the two solid phases. Line shape and spin-lattice relaxation rate studies of the ammonium headgroups and the adajacent methylene groups indicate the onset of alkyl-chain motion prior to the first order phase transition. In the low-temperature phase the line shape and the spin-lattice relaxation rates of the -ND3 groups are consistent with C3 jumps and an activation energy of 54±4 kJ mol-1. However, in the high-temperature phase the spin-lattice relaxation studies indicate the presence of small-angle diffusion of the -ND3 groups around the C3 symmetry axis. In this phase the -CD2- groups show line shapes typical of large-amplitude two-site jumps occurring at a rate > 107 s-1 . In the low-temperature phase, at temperatures below 295 K, the -CD2- 2H NMR line shapes indicate that the C - D bonds are essentially static

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