Rotational constants nuclear quadrupole coupling effect

The nuclear quadrupole interaction often produces measurable effects in electronic, rotational, atomic and molecular beam resonance, nuclear magnetic resonance, and MOssbauer spectra. In many cases it can be directly studied by nuclear quadrupole resonance (NQR). The magnitude of interaction is expressed by the nuclear quadrupole coupling constant, e2qQ/hy which is the product of Eq. (1) and (3) expressed as a frequency. 

Despite the importance of the nuclear quadrupole coupling in affecting the rotational spectra, the literature concerning the theoretical predictions of its related constants is rather limited. A significant example is provided by the recent investigation performed on the hyperfine structure in the rotational spectra of bromofluoromethane [75]. The experimental determination was supported by quantum chemical calculations of the nuclear quadrupole-coupling and spin-rotation tensors of Br and Br, performed at the CCSD(T) level in conjunction with core-valence correlation-consistent bases. Zero-point vibrational (ZPV) corrections were computed at the MP2 level in conjunction with the cc-pCVTZ basis set, whereas relativistic effects on the electric field gradient at the bromine... 

Yi and Ys - gyromagnetic ratio of spin 1 and spin S nuclear spin, rJS = intemuclear distance, tr= rotational correlation time, x< = reorientation correlation time, xj = angular momentum correlation time, Cs = concentration of spin S, Cq = e2qzzQ/h = quadrupole coupling constant, qzz = the electric field gradient, Q = nuclear electric quadrupole moment in 10 24 cm2, Ceff = effective spin-rotational coupling constant, a = closest distance of appropriate of spin 1 and spin S, D = (DA+DB)/2 = mutual translational self diffusion coefficient of the molecules containing I and S, Ij = moment of inertia of the molecule, Ao = a// - ol-... 

Chemists pay much less attention to the NMR relaxation rates than to the coupling constants and chemical shifts. From the point of view of the NMR spectroscopist, however, the relaxation characteristics are far more basic, and may mean the difference between the observation or not of a signal. For the quadrupolar nucleides such as 14N the relaxation characteristics are dominated by the quadrupole relaxation. This is shown by the absence of any nuclear Overhauser effect for the 14N ammonium ion despite its high symmetry, which ensures that the quadrupole relaxation is minimized. Relaxation properties are governed by motional characteristics normally represented by a correlation time, or several translational, overall rotational and internal rotational, and thus are very different for solids, liquids and solutions. 

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