Related Experiment Videos
"Cooking the sample": radiofrequency induced heating during solid-state NMR experiments
Jean-Baptiste d'Espinose de Lacaillerie1, Benjamin Jarry, Ovidiu Pascui
1Laboratoire de Physique Quantique, UMR CNRS 7142 SIEN, Ecole Supérieure de Physique et de Chimie Industrielles de la Ville de Paris, 10 rue Vauquelin, 75231 Paris, Cedex 05, France. Jean-Baptiste.dEspinose@espci.fr
Solid State Nuclear Magnetic Resonance
|October 14, 2005
Summary
Radiofrequency (RF) energy can heat samples in solid-state NMR, especially those with polar molecules. This RF heating can bias measurements of molecular motion dynamics and activation energy.
Area of Science:
- Nuclear Magnetic Resonance (NMR) Spectroscopy
- Physical Chemistry
- Materials Science
Background:
- Radiofrequency (RF) energy dissipation as heat in solid-state NMR is typically considered negligible.
- Dynamic Nuclear Magnetic Resonance (NMR) experiments, particularly those involving continuous wave decoupling, can lead to significant sample heating.
- This heating effect is pronounced in samples containing polar molecules and when RF power is applied for extended durations.
Purpose of the Study:
- To investigate the phenomenon of RF energy dissipation as heat during continuous wave decoupling in solid-state NMR.
- To identify the mechanisms responsible for RF energy deposition in polar samples.
- To assess the impact of RF-induced heating on dynamic NMR measurements and the determination of activation energies.
Main Methods:
- Investigated RF energy dissipation during continuous wave decoupling in solid-state NMR experiments.
- Examined temperature increases in dimethylsulfone (DMS) during CODEX pulse sequences to study methyl flip motion.
- Studied temperature increases in hydrated lead nitrate during high-power decoupling one-pulse experiments to identify RF energy deposition mechanisms.
Main Results:
- RF energy conversion to heat was shown to activate methyl flip motion in dimethylsulfone (DMS).
- This RF-induced heating introduced significant bias in correlation time-temperature dependency measurements for activation energy determination.
- RF energy deposition in hydrated lead nitrate was attributed to dielectric losses, similar to microwave heating.
- RF heating was confirmed in solid-state NMR experiments at moderate B0 fields for samples with polar molecules, including hydrated polymers and inorganic solids.
Conclusions:
- RF heating is a significant factor in solid-state NMR experiments involving polar molecules and prolonged RF power application.
- RF-induced heating can lead to systematic errors in measurements of slow molecular dynamics.
- Researchers must consider RF heating effects to ensure accurate interpretation of dynamic NMR data, especially when determining activation energies.