Nuclear spin relaxation in chloroform dissolved in a nematic phase: spectral densities at high-frequencies

Longitudinal relaxation data are reported for C-13 labelled CHCl3 in a nematic liquid crystalline solvent at several magnetic field strengths. Two-dimensional exchange spectroscopy has been applied together with transfer-modes analysis to obtain the relaxation matrix including the cross-correlation terms. The spectral densities were found to be frequency dependent, which is interpreted in terms of a fast local motion and a slow process, both contributing to relaxation. When taking this into account, the cross-correlation rates were found to be linear in the magnetic field, and they can be attributed to DD/CSA interference. In addition, a small field-independent contribution is found for H-1. This can be related to interference effects between intramolecular DD and intermolecular DD relaxation