Two-dimensional NMR of velocity exchange:: VEXSY and SERPENT

Two different multidimensional pulsed field gradient sequences are compared which have the purpose of correlating spin displacements in different time intervals with each other. The simplest possible sequence, three-pulse SERPENT, measures displacements in two interleaved time intervals, while in VEXSY, consisting of two independent pairs of gradient pulses separated by a mixing time, displacements during the two encoding intervals are compared to each other. The formalism for both sequences is discussed in q space and in displacement space and common features as well as differences between the two types of experiments are highlighted, employing the particular case of the concurrent VEXSY scheme which allows treatment according to both formalisms. (C) 2001 Academic Press.