Nuclear electric coupling

Nuclear electric quadrupole QCC (quadrupole coupling constant), (asymmetry parameter) Line-shape analysis, nutation NMR Coordination symmetry... 

Other key properties of these complexes relevant for comparison with experiment are the nuclear quadrupole coupling constants. Theoretical NQCC values, as calculated via electric field gradients, are discussed exhaustively in several recent theoretical investigations [26,28,30,33,34] and in experimental work [4-11]. BH HLYP/aug-cc-pVTZ calculated NQCCs [30,34], as evaluated for XY- -NH3 complexes, are listed in Table 10. 

It is evident that the operator Hd couples only the small components of the relativistic molecular wavefunctions. Since the small components as well as the nuclear electric fields are prominent in and around the nuclear regions, the dominant contribution to the matrix elements of Hj comes from that region. It should be noted that the absence of the screening term Eq in Eq.(42) will overestimate the //d matrix element. However, the amount of overestimation is expected to be small. 

A discussion of nuclear electric quadrupole coupling in the vinyl halides has led to the estimate of about 6 percent double-bond character for the C—Cl bond in vinyl chioride and 3 percent for the C—I bond in vinyl iodide.87 Values of electric dipole moments of mono-halogenated benzenes have been interpreted as corresponding to 4 percent of double-bond character for the C—X bonds.68... 

The interaction between the nuclear electric quadrupole moment and the electrons of the molecule couples the nuclear spin I to the rotational angular momentum J, giving a resultant total angular momentum F, of... 

Spin-spin relaxation (time T2) can result from both intermolecular homo-nuclear exchange coupling and dipole-dipole interactions, but only the latter is observable at Mn2+ concentrations <10-2 M. Mn2+ forms both inner- and outer-sphere complexes. In symmetrical inner-sphere complexes like Mn(H20)62+, the spin-spin coupling is strongly forbidden, T2 is long, and lines remain narrow. When nonsymmetric inner-sphere complexes form, the resulting anisotropy of the electric field leads to allowed spin-spin transitions that produce very small values of T2 and very broad, perhaps even unobservable, lines (56). 

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-... 

Carr-Purcell-Meiboom-Gill nuclear quadrupolar coupling constant receptivity relative to aH electric field gradient nuclear spin quantum number magic-angle spinning... 

X the 33S nuclear quadrupole coupling constant (expressed in frequency units), and r] the asymmetry parameter of the electric field gradient tensor (0[Pg.21]

S nuclear quadrupole coupling constants have been determined from line width values in some 3- and 4-substituted sodium benzenesulphonates33 63 and in 2-substituted sodium ethanesulphonates.35 Reasonably, in sulphonates R — SO3, (i) t] is near zero due to the tetrahedral symmetry of the electronic distribution at the 33S nucleus, and (ii) qzz is the component of the electric field gradient along the C-S axis. In the benzenesulphonate anion, the correlation time has been obtained from 13C spin-lattice relaxation time and NOE measurements. In substituted benzenesulphonates, it has been obtained by the Debye-Stokes-Einstein relationship, corrected by an empirically determined microviscosity factor. In 2-substituted ethanesulphonates, the molecular correlation time of the sphere having a volume equal to the molecular volume has been considered. 

In these studies, the parameters that could provide the most interesting information are likely to be the electric field gradient (nuclear quadrupole coupling constant) at the 33S nucleus and its asymmetry parameter. Indeed, modifications of the lattice structure in different cement matrixes are expected to influence the symmetry of the electronic distribution around the sulphur nucleus more than the chemical environment of sulphur. 

Quantum mechanical calculations of 33S nuclear quadrupole coupling constants are not an easy matter (not only for the 33S nucleus, but for all quadrupolar nuclei). Indeed, the electric field gradient is a typical core property, and it is difficult to find wave functions correctly describing the electronic distribution in close proximity to the nucleus. Moreover, in the case of 33S, the real importance of the Sternheimer shielding contribution has not been completely assessed, and in any case the Sternheimer effect is difficult to calculate. 

Nuclear hyperfine splittings in the rotational spectra of dimers have been observed in the molecular beam electric resonance experiments and the Fourier transform microwave experiments. In most cases, the coupling constants are interpreted with the simplified expression given in Eqn. (6) for axially symmetric molecules in the K=0 rotational manifold. Thus both the nuclear quadrupole coupling term and the... 

Nuclear Quadrupole Resonance (NQR) [50-54], Nuclear (electric) quadrupole resonance (NQR) was invented in 1950 [55] and is applicable to nuclei with nonzero nuclear electric quadrupoles eQ, which are 3x3 tensors, whose significant components are the quadrupole coupling constant QCC ... 

The most important examples of 2S states to be described in this book are CO+, where there is no nuclear hyperfine coupling in the main isotopomer, CN, which has 14N hyperfine interaction, and the Hj ion. A number of different 3E states are described, with and without hyperfine coupling. A particularly important and interesting example is N2 in its A 3ZU excited state, studied by De Santis, Lurio, Miller and Freund [19] using molecular beam magnetic resonance. The details are described in chapter 8 the only aspect to be mentioned here is that in a homonuclear molecule like N2, the individual nuclear spins (1 = 1 for 14N) are coupled to form a total spin, It, which in this case takes the values 2, 1 and 0. The hyperfine Hamiltonian terms are then written in terms of the appropriate value of h As we have already mentioned, the presence of one or more quadrupolar nuclei will give rise to electric quadrupole hyperfine interaction the theory is essentially the same as that already presented for1 + states. 

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