Nuclear field shift

Bigeleisen J (1949) The relative velocities of isotopic molecules. J Chem Phys 17 675-678 Bigeleisen J (1955) Statistical mechanics of isotopic systems with small quantum corrections. I. General considerations and the rule of the geometric mean. J Chem Phys 23 2264-2267 Bigeleisen J (1998) Second-order correction to the Bigeleisen-Mayer equation due to the nuclear field shift. Proc National Acad Sci 95 4808-4809... 

Eujii T, Suzuki D, Gunjii K, Watanabe K, Moriyama H, Nishizawa K (2002) Nuclear field shift effect in the isotope exchange reaction of chromium(III) using a crown ether. J Phys Chem A 106 6911-6914 Gale JD (2001) Simulating the crystal structures and properties of ionic materials from interatomic potentials. Rev Mineral Geochem 42 37-62... 

Rotational constants, centrifugal distortion constants, rotation-vibration interaction constants, Dunham energy parameters, Dunham potential coefficients, parameters of the breakdown of the Bom-Oppenheimer approximation and of the nuclear field shift, and equilibrium intemuciear distances. Eiectronic spin-rotation, spin-spin, spin-orbit, and /1-doubling parameters and their centrifugai-distortion corrections in excited electronic states... 

Nuclear volume effects, sometimes referred to as nuclear field shift effects, are believed to be one cause of mass-independent isotope fractionation [46]. Nuclei of isotopes differ from one another only in their number of neutrons. Self-evidently, this provides the isotopes with a different mass, but this may also give rise to differences in the size and shape of the nuclei among the isotopes. The nuclei of nuclides with an odd number of neutrons are often smaller than they should be based on the mass difference relative to those of the neighboring nuclides with an even number of neutrons [47]. These differences in nuclear shape and size, and thus charge density, affect the interaction between the nucleus and the surrounding electron cloud. The resulting difference between the isotopes in terms of density and shape of the electron cloud results in slight differences in the efficiency with which they participate in chemical reactions [48]. 

Fujii, T., Moynier, F., and AlbarMe, F. (2009) The nuclear field shift effect in chemical exchange reactions. Chem. Geol, 267, 139-158. 

A small amount of theoretical work has been published on the fractionation of uranium isotopes. As mentioned above, Schauble [64] demonstrated that equilibrium isotope fractionation between species of the heaviest elements is not dominated by differences in bond vibrational frequencies, as they are for lighter elements, but by the nuclear field shift effect. This effect is due to interactions between electron shehs, espedahy s shells, that have high electron density near the very large nuclei of heavy atoms. The heavier isotopes partition into those species with fewer s electrons or in which s electrons are shielded by more p, d, or f electrons. Schauble [64] presented calculations for various ojddation states and species of T1 and Hg and the same general conclusions apply to U. Calculations for uranium species were presented at a conference by Schauble ]73]. The largest fractionations are predicted to occur when U(IV) and U(VI) species equilibrate, with values of au(iv) u(vi) as large as 0.0012 at 273 K [Au(i iu(vi) l-2%o at 0°C]. U(IV) has two 5f electrons that apparently shield s electrons from the isotopically... 

More recently, Epov et al. [65] reviewed what is known about mechanisms of fractionation not due to mass-dependent differences in bond vibrational frequencies. These mechanisms include the nuclear field shift effect, but also the nuclear spin effect, which results from interaction between the magnetic field associated with a nucleus with nonzero spin (such as 2 U) and the magnetic fields associated with electron spin angular momentum. They pointed out that so far, no data unambiguously reflect this effect, but it is possible that fractionation of U in the contexts described here results from the nuclear spin effect, rather than the nuclear field shift effect. 

I have tried to present a picture of the richness of this rapidly developing field of isotope shift studies. Spectroscopists have long used the nuclear field shift to help in the classification of spectra by identifying the presence of penetrating electrons in a configuration. Here we saw how these penetrating electrons serve to Study nuclear structure. 

The equations to be fulfilled by momentum space orbitals contain convolution integrals which give rise to momentum orbitals ( )(p-q) shifted in momentum space. The so-called form factor F and the interaction terms Wij defined in terms of current momentum coordinates are the momentum space counterparts of the core potentials and Coulomb and/or exchange operators in position space. The nuclear field potential transfers a momentum to electron i, while the interelectronic interaction produces a momentum transfer between each pair of electrons in turn. Nevertheless, the total momentum of the whole molecule remains invariant thanks to the contribution of the nuclear momenta [7]. 

For molecules containing light atoms, we accordingly neglect this effect of finite nuclear volume or field shift, but other effects prevent exact application of isotopic ratios that one might expect on the basis of a proportionality with in formula 13 instead of total F. For this reason we supplement term coefficients in formula 8 for a particular isotopic species i with auxiliary coefficients [54],... 

S is the electron spin quantum number and E = gfiSiH. Nuclear resonance field shifts AH then are observed which are given by the expression... 

High-coordination-number complexes of 0-keto-enolates continue to be obtained with the metals such as zirconium(IV),8 hafnium(IV),8 cerium(IV),9 and the lanthanons(III),10 the last being tetrakis anionic species. At least one example of a volatile tetrakis 0-keto-enolate salt has been reported,11 Cs[Y(CF3-COCHCOCF3)4]. The ionic charge on the 0-keto-enolate complex has been shown to produce12 a high field nuclear magnetic resonance for anions and low field shifts for cations, relative to the positions observed for the neutral species. 

Holzman, G. R., P. C. Lauterbur, J. H. Anderson, and W. Koth Nuclear Magnetic Resonance Field Shifts of 2SSi in Various Materials. J. chem. Physics 25, 172—173 (1956). 

In the present context the former produces a nuclear resonance shift (the pseudocontact shift) whereas the latter only affects the relaxation behaviour. In the absence of chemical exchange and in cases when Tie r the local field experienced by the nucleus is given by ... 

The descriptions of the structure, energy, and dynamics of H-bonds continue to be a formidable task for both experimental and theoretical investigations. IR and nuclear magnetic resonance (NMR) techniques have become routine tools to analyze H-bonding interactions in various systems [1-4, 150]. The vibrational modes of molecules in the H-bonded state are affected in several ways. The proton involved in H-bonding interaction exhibits down field shift. Spectroscopic information obtained from these techniques has been used to probe H-bonding interactions. 

Nuclear magnetic resonance (NMR) spectroscopy has proven to be the most versatile technique to study organometallic compounds both non-aqueous and aqueous solutions [6, 7]. To explore all the possibilities of NMR one has to either work in DzO as solvent or use a water signal suppression technique. Proton chemical shifts can give information about the structure. Generally, protons bound to carbons coordinated to a metal center show a low-field shift, about 1-4 ppm, compared with the metal-free environment. Metal hydrides usually have negative... 

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