✍ Scribed by F.I. Bashirov
No coin nor oath required. For personal study only.
New symmetry-adapted autocorrelation functions are used in A 1/2 Å 3p 5 (N 0 1)g 4 ប 2 b 06 , [3] the theoretical description of the nuclear magnetic dipole-dipole relaxation in molecular crystals. They are obtained in the model frame that a molecule rotates by means of the finite angular jumps N is the number of the interacting spins, and all other conbetween the hindered states of the same symmetry in different stants have their usual meanings (1). The spectral densities potential wells. The experimental data of the temperature dependence of the proton relaxation times T 1 and T 1r in the mono-and J m (v) (m takes the values 0, 1, and 2) are Fourier transforms polycrystalline NH 4 Cl are revised. As a result, it is proposed to of the autocorrelation functions (ACFs) K m (t) of the secondclassify the NH / 4 ion motion by two kinds of the hindered states order normalized spherical harmonics Y (2) m (g) corresponding to the two-dimensional ( E) and three-dimensional (F) irreducible representations of a point group of the cubic system. The dynamical weight of the state F is defined to be equal J m (v) Å ͐ ϱ 0ϱ K m (t)exp(ivt)dt. [4] to 0.25 and that of the state E to be equal to 0.73 from the experiments in the ordered phase of NH 4 Cl. Based on abstract geometric groups, the respective weights are 0.4 and 0.6. This discrepancy in The ACFs depend on the character of the molecular motion. the weights of the states is explained by the effect of the tetragonal The thermal motion of rigid molecules in crystals may be distortion of the tetrahedral site symmetry of the NH / 4 ion. The described by either of two principal models: the rotational result of the prevalence of a C 3 reorientation in comparison to a diffusion model (1-3) or the model of angular jumps be-C 2 reorientation of the ion is also justified. Because of the absence tween spatially fixed orientations (4-11). The approximaof the experimental temperature minima of T 1 or T 1r , assumptions tion of the molecular hindered motion in solids by means are only made about the dynamical parameters of the NH / 4 ion of these two models has shown their validity in some polymotion in the disordered phase of NH 4 Cl.
📜 SIMILAR VOLUMES
## Proton spin-lattice relaxation time constants (TV) have been found to range over more than an order of magnitude for coals of different rank'-'. Proposed relaxation mechanisms have included spin diffusion to paramagnetic centreslm3 or to rotating methyl groups5, and penetration of molecular ox