title: Separation of isotropic chemical and second-order quadrupolar shifts by multiple-quantum double rotation NMR.
abstract: Using a two-dimensional multiple-quantum (MQ) double rotation (DOR) experiment the contributions of the chemical shift and quadrupolar interaction to isotropic resonance shifts can be completely separated. Spectra were acquired using a three-pulse triple-quantum z-filtered pulse sequence and subsequently sheared along both the nu(1) and nu(2) dimensions. The application of this method is demonstrated for both crystalline (RbNO(3)) and amorphous samples (vitreous B(2)O(3)). The existence of the two rubidium isotopes ((85)Rb and (87)Rb) allows comparison of results for two nuclei with different spins (I=3/2 and 5/2), as well as different dipole and quadrupole moments in a single chemical compound. Being only limited by homogeneous line broadening and sample crystallinity, linewidths of approximately 0.1 and 0.2 ppm can be measured for (87)Rb in the quadrupolar and chemical shift dimensions, enabling highly accurate determination of the isotropic chemical shift and the quadrupolar product, P(Q). For vitreous B(2)O(3), the use of MQDOR allows the chemical shift and electric field gradient distributions to be directly determined-information that is difficult to obtain otherwise due to the presence of second-order quadrupolar broadening.
authors.affiliation: Physics Department, University of Warwick, Coventry, UK.
authors.forename: Ivan
authors.initials: I
authors.lastname: Hung
authors.forename: Alan
authors.initials: A
authors.lastname: Wong
authors.forename: Andy P
authors.initials: AP
authors.lastname: Howes
authors.forename: Tiit
authors.initials: T
authors.lastname: Anupõld
authors.forename: Ago
authors.initials: A
authors.lastname: Samoson
authors.forename: Mark E
authors.initials: ME
authors.lastname: Smith
authors.forename: Diane
authors.initials: D
authors.lastname: Holland
authors.forename: Steven P
authors.initials: SP
authors.lastname: Brown
authors.forename: Ray
authors.initials: R
authors.lastname: Dupree
mesh_terms: D000465:Algorithms; D001895:Boron; D001896:Boron Compounds / Q000737:chemistry; D003460:Crystallization; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011868:Radioisotopes; D012413:Rubidium / Q000737:chemistry; D012414:Rubidium Radioisotopes
chemical_list: D001896:Boron Compounds; D011868:Radioisotopes; D012414:Rubidium Radioisotopes; C042168:boron oxide; D012413:Rubidium; D001895:Boron