Electron charge shift

Scheme 9.2 The electron charge shift for Y-Z bonds the case of CF3CI and H2O molecules is presented arrows show the electron charge shifts...

Figure 9.11 presents for the same sample of hydrogen bonds the correlations between the electron charge shift from the Lewis base to the Lewis acid and different... 

F. 9.11 The cotrelation between the electron charge shift (an) and energy (kcal/mol) open circles are related to —Ebjn ena-gy (Ebjn is the binding energy), full circles to -CT (charge transfer DFT/NEDA energy) while fiiU squares correspond to the part of CT, i.e. the nn -< 0 orbital-orbital intoaction en gy... 

Studies of electronic charge shift in acetylenes have been made using n.m.r. spectra. The isolation, characterization, and synthesis of many naturally occurring acetylenes and polyacetylenes have been reported by Bohlmann and his group. ... 

Raman spectra have also been reported on ropes of SWCNTs doped with the alkali metals K and Rb and with the halogen Br2 [30]. It is found that the doping of CNTs with alkali metals and halogens yield Raman spectra that show spectral shifts of the modes near 1580 cm" associated with charge transfer. Upshifts in the mode frequencies are observed and are associated with the donation of electrons from the CNTs to the halogens in the case of acceptors, and downshifts are observed for electron charge transfer to the CNT from the alkali metal donors. These frequency shifts of the CNT Raman-active modes can in principle be u.sed to characterise the CNT-based intercalation compound for the amount of intercalate uptake that has occurred on the CNT wall. 

Figure 6.11 A comparison of inductive stabilization for methyl, primary, secondary, and tertiary carbocations. The more alkyl groups there are bonded to the positively charged carbon, the more electron density shifts toward the charge, making the charged carbon less electron-poor (blue in electrostatic potential maps).

The electric monopole interaction between a nucleus (with mean square radius k) and its environment is a product of the nuclear charge distribution ZeR and the electronic charge density e il/ 0) at the nucleus, SE = const (4.11). However, nuclei of the same mass and charge but different nuclear states isomers) have different charge distributions ZeR eR ), because the nuclear volume and the mean square radius depend on the state of nuclear excitation R R ). Therefore, the energies of a Mossbauer nucleus in the ground state (g) and in the excited state (e) are shifted by different amounts (5 )e and (5 )g relative to those of a bare nucleus. It was recognized very early that this effect, which is schematically shown in Fig. 4.1, is responsible for the occurrence of the Mossbauer isomer shift [7]. 

The electron density i/ (0)p at the nucleus primarily originates from the ability of s-electrons to penetrate the nucleus. The core-shell Is and 2s electrons make by far the major contributions. Valence orbitals of p-, d-, or/-character, in contrast, have nodes at r = 0 and cannot contribute to iA(0)p except for minor relativistic contributions of p-electrons. Nevertheless, the isomer shift is found to depend on various chemical parameters, of which the oxidation state as given by the number of valence electrons in p-, or d-, or /-orbitals of the Mossbauer atom is most important. In general, the effect is explained by the contraction of inner 5-orbitals due to shielding of the nuclear potential by the electron charge in the valence shell. In addition to this indirect effect, a direct contribution to the isomer shift arises from valence 5-orbitals due to their participation in the formation of molecular orbitals (MOs). It will be shown in Chap. 5 that the latter issue plays a decisive role. In the following section, an overview of experimental observations will be presented. 

Figure 2.10. An example of electron flood gun treatment of XPS charging shifts of O (Is) lines from a silica specimen. The effect of increasing flood gun current is shown. (After Barr, 1983.)...

Such a rate increase at short distances has been observed also by M.E. Michel-Beyerle [12] in time resolved experiments with a photoactivated acri-dinium ion as electron acceptor. This effect can be explained by the influence of the distance on the solvent reorganization energy The solvent reorganization energy is small for charge shifts over short distances, and it increases with the distance until it reaches a plateau. In this plateau area the solvent reorganization energy remains constant and Eq. (1) can be applied ... 

This moment measures the extent and direction of the shift of an atom s electronic charge cloud with respect to the nucleus. The quantity M(fi) can effectively be regarded as an intra-atomic dipole moment. The intra-atomic dipole moment of each atom contributes to the... 

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