NMR study of molecular dynamics and phase transitions in dimethyl ammonium hexabromo selenate [NH2(CH3)2]2SeBr6

✍ Scribed by B.V.S. Murthy; K.P. Ramesh; J. Ramakrishna

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 126 KB
• Volume: 61
• Category: Article
• ISSN: 0022-3697
• DOI: 10.1016/s0022-3697(99)00396-0

✦ Synopsis

H spin lattice relaxation study in the temperature range 439-77 K has been carried out in dimethyl ammonium (DMA) hexabromo selenate. A high temperature phase transition is observed as a dip in T 1 around 360 K, followed by a slope change at 222 K, and a discontinuous jump in T 1 at 154 K, which are also attributed to phase transitions. DMA diad axis motion and spinrotation interaction are found to be the dominant mechanisms responsible for the observed T 1 behaviour above 222 K, while between 222 and 154 K, DMA torsional oscillations contribute significantly. Below 154 K the relaxation is governed by the methyl group dynamics. The motional effects are also reflected in the second moment variation with temperature.