Einfluß der Heternuklearen Entkopplung auf die Ergebnisse dynamischer Festkörper-NMR-Experimente

Dissipation of radiofrequency (rf) energy as heat during continuous wave decoupling in solid-state NMR experiment is examined. A significant temperature increases can occur while performing dynamic NMR measurements provided the sample is polar contains polar molecules and the sequence calls for relatively long applications of rf decoupling power. It is shown that the methyl flip motion in dimethyl sulfone (DMS) is activated by the decoupling rf energy deposition as heat into the sample during a CODEX pulse sequence. This introduces a significant bias in the correlation time-temperature dependency measurement used to obtain the activation energy of the dynamic. By investigating the dependency of the temperature increase in hydrated lead nitrate on experimental parameters during high-power one-pulse experiments, the mechanisms for the RF energy deposition is identified. The samples heat due to dissipation of the energy absorbed by dielectric losses, a phenomenon commonly known as microwave heating. It is thus established that during common solid-state NMR experiments at moderate B0 fields, RF heating leads to the heating of samples containing polar molecules such as polymers and hydrated inorganic solids. In particular, this can results in systematic errors for dynamics measurements by solid-state NMR where the spin system is prepared by an evolution periods utilising strong proton decoupling