Osborn Popp, Thomas M., Alexander Däpp, Chukun Gao, Pin-Hui Chen, Lauren E. Price, Nicholas H. Alaniva, and Alexander B. Barnes. “Highly Stable Magic Angle Spinning Spherical Rotors Lacking Turbine Grooves.” Preprint. Solid-state NMR/Instrumentation, April 1, 2020.
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 simple retroﬁtting of a commercial NMR probe with MAS spheres for solid-state NMR. We analyze a series of turbine groove 5 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.