DIRECT MEASUREMENT OF TRANSVERSE RELAXATION TIME OF INTERMOLECULAR MULTIPLE QUANTUM COHERENCES IN NMR

A one-dimensional NMR method is presented for measuring the transverse relaxation time, T_2,n, of intermolecular multiple quantum coherences (IMQCs) of coherence order n in highly polarized spin systems. The pulse sequence proposed in this paper effectively suppresses the effects of radiation damping, molecular diffusion, inhomogeneity of magnetic field, and variations of dipolar correlation distance, all of which may affect quantitation of T_2,n. This pulse sequence can be used to measure not only IMQC transverse relaxation time T_2,n (n>1) quickly and directly, but also the conventional transverse relaxation time. Experimental results demonstrate that the quantitative relationship between T_2,n (n≥1) and T₂ is T_2,n ≈T₂/n. These results will be helpful for understanding the fundamental properties and mechanisms of IMQCs.