Structural Phase Transition of N,N-Dimethylnitramine as Studied by 14N Nuclear Quadrupole Resonance

Abstract

Abstract The 14N nuclear quadrupole relaxation time and resonance frequencies v+, v-, and vd of N,N-dimethylnitramine were measured between 14 and 313 K. The frequency increase of v+ and v- observed below Tc (108 K) is explained by the increase of p π electrons in the amino nitrogen caused by the deformation of the molecular skelton, which is planar above Tc. The sharp T1Q minima for v+ and v- observed at Tc are attributed to the softening of vibration modes on both sides of Tc. The fluctuation o f the nitrogen-hydrogen magnetic dipolar interaction due to CH3 reorientation was detected as a broad T1Q minimum observed around 84 K. A logarithmic divergence of T1Q -1 observed on the high-temperature side of Tc suggests the presence of a diffusive or overdamped-type soft mode.