Effect of cross polarization radiofrequency phases on signal phase

• Published in: Solid state nuclear magnetic resonance Vol. 117; p. 101771
• Main Authors: Shekar, S. Chandra, Zhao, Wancheng, Weldeghiorghis, Thomas K., Wang, Tuo
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 01.02.2022
• Subjects: CP MAS; Evolution operator; Fast molecular rotation; RF phases; Signal phase; Solid-state NMR; Signal phase; Solid-state NMR; Fast molecular rotation; Evolution operator; CP MAS; RF phases
• ISSN: 0926-2040; 1527-3326
• DOI: 10.1016/j.ssnmr.2021.101771

Utilizing phases of radio frequency (RF) pulses to manipulate spin dynamics is routine in NMR and MRI, leading to spectacular techniques like phase cycling. In a very different area, cross polarization (CP) also has a long history as part of a vast number of solid-state NMR pulse sequences. However, a detailed study devoted to the effect of CP RF phases on NMR signal, seems not to be readily available. From first principles, we arrive at a simple dependence of NMR signal on arbitrary CP RF phases, for static and MAS conditions, accompanied by experimental verification. In the process, the CP propagator emerges as a product of RF “pulses” and a period of “free precession”, conforming to coherence transfer pathway theory. The theoretical expressions may lend confidence for dealing with CP blocks with tunable phases in pulse sequences. [Display omitted] •Effect of arbitrary RF phases during CP NMR explored from first principles.•S-spin NMR signal acquires same phase as arbitrary RF phases during CP.•This holds for both static and MAS, as evolution operator structure is preserved.•Extensively experimentally validated for 1H-X(=13C, 15N, 31P) CP (static and MAS).