NMR relaxation study of methyl groups in solids from low to high temperatures

Abstract

ABSTRACT:The calculation of the correlation functions of complex motion consisting of jumps over the barrier (classical motion) and jumps through the barrier (incoherent tunneling) is presented. The Schrö dinger equation has been applied in the calculation of the rate constant of tunneling jumps through the barrier. This rate constant determines directly the temperature at which incoherent tunneling ceases. The calculated spectral densities are applied to analyze the temperature dependencies of the spin-lattice relaxation rate in solids containing a methyl group.

Complex dynamics of 1.3.5-trimethylbenzene-2.4.6-D3 studied by proton spin–lattice NMR relaxation and second moment of NMR line

“…11 in Ref. [17]). Moreover n T (1/ ) v A Ev 1 1 1 can be neglected because the population of molecules at v 1 is small (see Fig.…”

“…1 was previously assumed for protons in Refs. [16,17]. This value followed from the assumed value L ¼1.78 Å as the barrier width, which is the distance between protons in methyl group.…”

“…The expression for the tunnelling correlation time has been derived in Refs. [16,17] and it follows from the Schrodinger equation:…”

“…The approach assumed in papers [16][17][18] is based on the method of calculation of the total correlation function for a complex motion [15]. The C 3 motion of the methyl group is composed of the jumps over the barrier and through the barrier, taking place with different probabilities.…”

Complex methyl groups dynamics in [(CH3)4P]3Sb2Br9 (PBA) from low to high temperatures by proton spin–lattice relaxation and narrowing of proton NMR spectrum

“…The method to derive the total correlation function of a complex motion used earlier in [24][25][26][27][28] is applied to the calculations of the complex methyl group motion spectral density. The Arrhenius temperature dependence is assumed for the correlation time of the classical C 3 rotation of the methyl group.…”