Low-field approach to double resonance in nuclear quadrupole resonance of spin-1 nuclei

摘要

Using double-resonance conditions,in which the Larmor frequency of a spin-1/2 nucleus is matched to one of the nuclear quadrupole resonance frequencies of a spin-1 nucleus,the authors demonstrate increased cross relaxation between the two nuclear spin species.They calculate the cross-relaxation rate using the motionally averaged heterogeneous dipole Hamiltonian as a perturbation to the combined quadrupole and Zeeman Hamiltonians.Using this cross-relaxation rate,in addition to hydrogen and nitrogen autorelaxation rates,expressions governing spin-1/2 and spin-1 spin-lattice relaxation are determined.With ammonium nitrate,containing nitrogen (spin-1) and hydrogen (spin-1/2),increased nitrogen signal and spin-lattice relaxation are demonstrated,using fields less than 120 G.The cross-relaxation rate is also measured and an overall signaloise improvement by a factor of 2.3+0.1 is attained.