The Journal of Chemical Physics, 07 September 2012, Vol.137(9)
Effects of spin-spin interactions on the nuclear magnetic relaxation dispersion (NMRD) of protons were studied in a situation where spin ½ hetero-nuclei are present in the molecule. As in earlier works [K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, J. Chem. Phys. 129 , 234513 ( 2008 ) 10.1063/1.3040272 ; S. E. Korchak, K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, J. Chem. Phys. 133 , 194502 ( 2010 ) 10.1063/1.3495988 ] , spin-spin interactions have a pronounced effect on the relaxivity tending to equalize the longitudinal relaxation times once the spins become strongly coupled at a sufficiently low magnetic field. In addition, we have found influence of 19 F nuclei on the proton NMRD, although in the whole field range, studied protons and fluorine spins were only weakly coupled. In particular, pronounced features in the proton NMRD were found; but each feature was predominantly observed only for particular spin states of the hetero-nuclei. The features are explained theoretically; it is shown that hetero-nuclei can affect the proton NMRD even in the limit of weak coupling when (i) protons are coupled strongly and (ii) have spin-spin interactions of different strengths with the hetero-nuclei. We also show that by choosing the proper magnetic field strength, one can selectively transfer proton spin magnetization between spectral components of choice.