Highly Stable Magic Angle Spinning Spherical Rotors Lacking Turbine Grooves

Abstract

Abstract. The use of spherical rotors for magic angle spinning offers a number of advantages including improved sample exchange, efficient microwave coupling for dynamic nuclear polarization nuclear magnetic resonance (NMR) experiments and, most significantly, high frequency and stable spinning with minimal risk of rotor crash. Here we demonstrate the sim- ple retrofitting of a commercial NMR probe with MAS spheres for solid-state NMR. We analyze a series of turbine groove geometries to investigate the importance of the rotor surface on spinning performance. Of note, rotors lacking any surface modification spin rapidly and stably even without feedback control. The high stability of a spherical rotor about the magic angle is shown to be dependent on its inertia tensor rather than the presence of turbine grooves.