OBSERVATION OF BULK SUSCEPTIBILITY EFFECTS IN HIGH-RESOLUTION NUCLEAR-MAGNETIC-RESONANCE

The phenomenon of multiple echoes following a two-pulse stimulated-ech o experiment in highly polarized systems is reinvestigated and explain ed using the Bloch equations. A semiquantitative formalism based on th e nuclear contributions to the magnetic susceptibility throughout a mu ltiple-pulse sequence is outlined and used to understand the formation of the echoes. This theory is used to direct the design of phase-cycl ed and pulsed-field-gradient experiments to control the echo formation . The theory also suggests a means of indirectly detecting a heteronuc leus contained in a different molecule. This kind of detection is acco mplished by modifying the static magnetic field with a stimulated-echo experiment on one set of the spins. Heteronuclear experiments show th at this classical semiquantitative formalism is a useful tool in the u nderstanding of spin dynamics in highly polarized systems. (C) 1996 Ac ademic Press, Inc.