Nuclear magnetic double resonance for a spin system subject to scalar relaxation of the second kind

Abstract

The equation of motion of a reduced spin density operator characterizing the state of a group of spins scalar coupled to a second group of spins which are either relaxing rapidly and/or irradiated with a strong radiofrequency field is derived within the framework of the non-viscous liquid approximation. An analytic expression for the spectral densities entering this equation is derived within the extreme narrowing approximation for the case in which the relaxation rates of the nuclei in the second group of spins are much greater than any scalar couplings between them. The resultant equation is used to discuss the conditions needed in a high resolution nuclear magnetic double resonance experiment to decouple a spin-½ nucleus (A) from a rapidly relaxing quadrupolar nucleus (X) in the fast relaxation limit, defined by |2πJAX T 1X | ≪ 1, in which the A resonance consists of a single broadened line. It is found that, if (ω A - ω X )2 ≫ T 1X -2 so that the x and y components of the JAX coupling can be neglected...