Nuclear magnetic resonance (NMR)

The energy difference of these Zeeman levels corresponds to the Larmor frequency, which is typically in the MHz regime. A weaker alternating magnetic field B1, which is applied in form of short pulses, will cause transitions between the Zeeman levels if the resonance condition is fulfilled. The B0 field is produced by large superconducting coils, which are cooled by liquid helium. The B1 field is generated by a small coil, which is wound around the sample and belongs to a resonant circuit.

Insights into molecular dynamics

When using NMR spectroscopy to investigate molecular dynamics, we exploit the fact that the interactions of the nuclear magnetic moments with additional internal fields lead to a dependence of the Zeeman levels and, thus, of the resonance frequencies on the molecular orientations and positions. Hence, molecular rotational and translational dynamics result in a detectable time dependence of the nuclear resonance frequencies.

Our applications

We combine various NMR methods to investigate molecular dynamics in wide ranges of time and length scales. For example, field-cycling relaxometry enables studies of fast motions from the pico- to microseconds regimes and stimulated-echo experiments provide access to slow dynamics in the micro- and milliseconds ranges. Like in clinical imaging applications (MRI), we can additionally apply magnetic field gradients to render the resonance frequency position dependent. We exploit this possibility to measure molecular diffusion coefficients. Furthermore, we use the spatial variation of the resonance frequency to perform spatially resolved studies on structurally inhomogeneous composite materials.