Intermolecular zero-quantum coherences of multi-component spin systems in solution NMR

Intermolecular zero-quantum coherences (iZQC) induced by the dipolar demagnetizing field can give both P- and N-type cross peaks. This paper shows that the relative intensities of the two types of iZQC peaks follow a simple relation, tan(2) (theta/2), from both the quantum (spin density matrix) and classical (modified Bloch equation) calculations. The experimental data and numerical simulations agree well with the prediction. In addition, higher-order iZQCs are experimentally examined for the first time and are explained by the quantum picture in which dipolar couplings convert four-spin operators into observable magnetization. (C) 1998 Academic Press.