Nuclear Resonance Absorption in Hydrated Crystals: Fine Structure of the Proton Line

Abstract

Fine structure has been observed in the nuclear paramagnetic resonance absorption line for protons in crystalline hydrates. The magnetic field of 6820 gauss was provided by a permanent magnet, the inherent stability of which facilitated detailed study of line shape. Measurements on a single crystal of CaSO4·2H2O show a splitting into four component lines with maximum separation varying from zero to 22 gauss, depending upon the direction of the externally applied magnetic field in the crystal. Both the number of component lines and the dependence of their spacing on field direction are calculated by treating the magnetic dipole-dipole interaction as a perturbation of the proton two-spin system within the water molecule; the effect of the more distant protons, neglected in this calculation, gives a finite width to the component lines. Variation of the splitting with field direction determines the orientation of the line joining protons in the water molecule, which is found to be consistent with positions ascribed to hydrogen nuclei in the lattice through simple considerations of chemical bonding. The distance between protons in the water molecule is measured by the splitting to be 1.58A for CaSO4·2H2O; if one assumes an H–O–H bond angle of 108°, the O–H distance is 0.98A. Powdered hydrates show a characteristic fine structure arising from isotropic distribution in solid angle of single crystal granules. This type of fine structure determines the proton-proton distance somewhat less accurately than does the single crystal experiment.

Nutation NMR Studies of Polyacetylene

“…The rest of the spectrum is the Pake doublet expected from the splitting of two 13 C dipoles. 7 This pattern can be fit to obtain directly the distance between the two dipoles, the desired carbon-carbon bond length. 5 ' 6 In this case the value obtained is 1.38+±0.02A.…”

Intertube effects on one-dimensional correlated state of metallic single-wall carbon nanotubes probed by C13 NMR

“…We found from NMR measurements under a magnetic field of 4 Tesla that the splitting is magnetic field independent (not shown), which is one of the characteristics of the well-known Pake doublets. 34 From the splitting we can estimate the carbon-carbon (C-C) bond length as follows. Here, we neglect the curvature of a graphene sheet and assume that the local structure around a 13 C atom with three 13 C nearest neighbors is a hexagonalhoneycomb plane for simplicity.…”

Intermediate dipolar distances from spin labels

“…(2) or (3) over all angles h. With a fixed separation between spins, this yields the so-called Pake pattern [14] that is characterized by sharp discontinuities at AEDH dd ð90 Þ and outer shoulders at AEDH dd ð0 Þ. The profile of the Pake pattern is given by the identity: I(DH dd ) Á dDH dd = sin h Á dh, which corresponds to the angular distribution for axial symmetry.…”