Pulsed Field Gradient Nuclear Magnetic Resonance as a Probe of Liquid State Molecular Organization

The imposition of magnetic field gradients on a nuclear magnetic resonance experiment imparts a spatial tag to the molecules via the Larmor frequencies of the nuclei (commonly protons) within. A sensitive measure of changes in the frequency distribution is afforded by detecting the loss of phase coherence in a spin-echo experiment performed in the presence of gradient pulses. Here the molecular displacements may be measured over the duration given by the pulse separation. Pulsed field gradient nuclear magnetic resonance (PFGNMR) employs timesca1es of tens of milliseconds and has a displacement sensitivity of the order 100 nm.