Topic
Nuclear quadrupole resonance
About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.
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TL;DR: In this article, the sp2 hybridization of the nitrogen σ bonding and lone-pair orbitals was analyzed for pyridazine, pyrazine, and pyrimidine.
Abstract: Nitrogen−14 nuclear quadrupole resonance data are reported for pyridazine, pyrazine, and pyrimidine. The spectra are analyzed assuming sp2 hybridization of the nitrogen σ bonding and lone‐pair orbitals. Coupling constants and asymmetry parameters are interpreted in terms of electron densities in σ and π orbitals and compared with values for pyridine. Evidence is presented indicating significant polarization of the σ bonds and strong localization of the lone‐pair electrons. Good agreement is found with LCAO MO calculations of π‐charge densities.
63 citations
TL;DR: In this paper, the effect of the charge differentiation introduced by the substitution of Sr for La has been attributed to the presence of 63/65 Cu resonances due to nonequivalent Cu sites.
Abstract: Nuclear magnetic/quadrupole resonance (NMR/NQR) has been observed for the Cu nuclei in La 2- x Sr x CuO 4 . NMR measurements have been carried out for the powdered sample whose c axes are aligned. No evidence for magnetic ordering was observed down to 1.3 K. Instead, the existence of two sets of 63/65 Cu resonances due to nonequivalent Cu sites has been concluded from the results of spectrum and relaxation measurements at low temperatures. These resonances are ascribed to the effect of the charge differentiation introduced by the substitution of Sr for La.
63 citations
63 citations
63 citations
TL;DR: These features are not manifestations of disturbances of the lattice by interstitial dopants, but are the intrinsic response of La[sub 2]CuO[sub 4+[delta]] to doped holes.
Abstract: We employ [sup 139]La NMR spectroscopy as a structural probe of metallic La[sub 2]CuO[sub 4+[delta]]. We find a distribution of lateral displacements of the oxygen atoms which form the apices of the oxygen octahedra. We directly observe a wide distribution of structures of the La-O layer; this distribution is strongly temperature dependent. We present copper NQR spectra which reveal a second, unexplained, copper site in the CuO[sub 2] planes. We show that these features are not manifestations of disturbances of the lattice by interstitial dopants, but are the intrinsic response of La[sub 2]CuO[sub 4+[delta]] to doped holes.
63 citations