title: RF inhomogeneity and how it controls CPMAS.
abstract: In this report we discuss the effect of radiofrequency field (RF) inhomogeneity on cross-polarization (CP) under magic-angle spinning (MAS) by reviewing the dependence of the CP-detected signal intensity as a function of the position in the sample space. We introduce a power-function model to quantify the position-dependent RF-amplitude profile. The applicability of this model is experimentally verified by nutation spectra obtained by direct signal detection, as well as by CPMAS signal detection, in two commercial MAS probes with different degrees of RF inhomogeneity. A conclusion is that substantial sections of a totally filled rotor, even in a probe with rather good homogeneity, do not contribute at all to the detected spectra. The consequence is that in CPMAS-based recoupling experiments, such as the CP-with-variable-contact-time (CPVC), spatial selectivity of the Hartmann-Hahn matching condition overcomes complications that could be caused by RF inhomogeneity permitting determination of accurate spectral parameters even in cases with high inhomogeneity.
authors.affiliation: Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA.
authors.forename: Rupal
authors.initials: R
authors.lastname: Gupta
authors.affiliation: Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA.
authors.forename: Guangjin
authors.initials: G
authors.lastname: Hou
authors.affiliation: Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA.
authors.forename: Tatyana
authors.initials: T
authors.lastname: Polenova
authors.affiliation: Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA. Electronic address: lexvega@comcast.net.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Vega
mesh_terms: D000465:Algorithms; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011846:Radio Waves
keywords: CPMAS; Cross polarization; Dipolar recoupling; Magic angle spinning; RF inhomogeneity