Multi-quantum quadrupole relaxation enhancement effects in Bi compounds.

H spin-lattice nuclear magnetic resonance relaxation experiments have been performed for triphenylbismuth dichloride (CHBiCl) and phenylbismuth dichloride (CHBiCl) in powder. The frequency range of 20-128 MHz has been covered. Due to H-Bi dipole-dipole interactions, a rich set of pronounced Quadrupole Relaxation Enhancement (QRE) peaks (quadrupole peaks) has been observed. The QRE patterns for both compounds have been explained in terms of single- and double-quantum transitions of the participating nuclei. The analysis has revealed a complex, quantum-mechanical mechanism of the QRE effects. The mechanism goes far beyond the simple explanation of the existence of three quadrupole peaks for N reported in literature. The analysis has been supported by nuclear quadrupole resonance results that independently provided the Bi quadrupole parameters (amplitude of the quadrupole coupling constant and asymmetry parameter).