A stimulated-echo method for diffusion measurements in heterogeneous media using pulsed field gradients

The pulsed-field-gradient stimulated-echo method is a well-established technique for studying molecular motion without disturbing the system under investigation. In porous media, the effects from internal magnetic field gradients make it necessary to perform compensatory sequences. Short relaxation times make it necessary to use as short pulse a sequence as possible. Here a pulse sequence which gives reliable diffusion measurements without the need for orthogonal spoiler gradients is presented, and the number of pi/2 and pi pulses is kept at a minimum. Experimental verification for the removal of unwanted echoes using the proposed PEGSTE sequence is provided, and preliminary diffusion measurements for ethane in a saturated H-ZSM5 zeolite are presented. (C) 1997 Academic Press.