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

In this paper a formula for the correlation function and spectral density of the complex motion made of the above-mentioned four components was derived and used in interpretation of the T1 relaxation time. The second moment of proton NMR line at temperatures below 50 K is four times lower than its value for the rigid structure. The three components of the internal motion characterized by τT, τH, and τiso were proved to reduce the second moment of the NMR line. The tunnel jumps of the methyl group reduce M2 at almost 0 K, the classical jumps over the barrier reduce M2 in the vicinity of 50 K, while the isotropic motion near 150 K. Results of the study on the dynamics of CH3 groups of TMP cation based on the second moment measurements were correlated with those based on T1 time measurements.