Oxygen nuclei

However, drastic consequences may arise if the nuclear spin is 0 or In these cases, some rovibronic states cannot be observed since they are symmetry forbidden. For example, in the case of C 02, the nuclei are spinless and the nuclear spin function is symmetric under permutation of the oxygen nuclei. Since the ground electronic state is only even values of J exist for the ground vibrational level (vj, V3) = (OO O), where (vi,V2,V3) are the... 

Figure 2.6. The tetrahedral structures of ice (a), (fc) are planes through sheets of selected oxygen nuclei (open circles), hydrogen nuclei (shotm in the insert as solid circles) are not shown in the main drawing. The insert illustrates the overlap of oxygen line pairs and the hydrogen nuclei, thus forming the hydrogen bonds (dotted lines)...

In sodium formate, and in various COOH groups, the distance between the carbon oxygen nuclei is found to be about 1.27 angstroms, the O—C—O angle being in neighborhood of 125°. L. Pauling, The Nature of the Chemical Bond, 2d ed., 32, Cornell University Press, 1940. 

The mechanism of ion transport in the MEEP/metal salt complexes has been modelled on the PEO transport mechanism, that is to say in terms of jumps of the metal ion between the ether oxygen nuclei of the side groups, the nitrogen atoms of the backbone being not involved in the coordination [599]. 

Figure 10-30 shows the constmction of the 2 -based molecular orbitals. One pair of MOs forms from the p orbitals that point toward each other along the bond axis. By convention, we label this as the z-axis. This end-on overlap gives Cp and

Figure 6.13 Relief map of the electron density for methanal (formaldehyde) in the molecular plane. There is a bond critical point between the carbon and the oxygen nuclei, as well as between the carbon nucleus and each hydrogen nucleus. No gradient path or bond critical point can be seen between the two hydrogen nuclei because there is no point at which the gradient of the electron density vanishes. There is no bond between the hydrogen atoms consistent with the conventional picture of the bonding in this molecule.

Hyperfine coupling constant, 22 267, 269 Hyperfine interaction, ESR data for, 22 274 Hyperfine parameters for O, 32 128-130 Hyperfine splitting, 31 81 Hyperfine structure, trimer species, 31 98-99 Hyperfine tensor, 22 267, 273-279, 336, 340 constants, 32 20-21 dioxygen species, 32 18-25 equivalent oxygen nuclei, 32 18-21 ionic oxides, 32 40... 

The effective distances obtained by Nordenskiold et al. (40) are compared with the internuclear distances in Table I. Clearly, the point dipole approximation is reasonable for the hydrogen nuclei in these complexes, while substantial deviations are observed for the oxygen nuclei. The findings of these early quantum chemical studies were confirmed by Sahoo and Das (41-43). Wilkens et al. have reported DFT calculations using Eq. (16) for a 104 atom model for high-spin Fe(III) rubredoxin (44). Large discrepancies between the effective distances and the input distances for the calculations were found for the hyperfine-shifted nitrogen-15 resonances, as well as for proton and carbon-13 nuclei in cysteines bound to the iron center. 

When we will discuss the effects of solvent collapse in solute-solvent interactions (section 8.11.2), we will mean local modifications of the water structure (degree of distortion of the oxygen bond distance between neighboring oxygen nuclei) induced by the presence of electrolytes in solution. We refer to the classical text of Eisemberg and Kauzmann (1969) for a more detailed discussion on the various aggregation states of the H2O compound. 

Angles 0 and 4> in equation 9.13 define the dipole orientation with respect to a coordinate system centered on the oxygen nuclei. The second term on the right... 

The most important reaction product here is silicon-28, which results from the addition of two oxygen nuclei accompanied by the loss of one helium nucleus. 

Eberhardt et al. (22a) have studied the photoemission of oxygen physi-sorbed on graphite at 10 K. The photoemission spectra exhibit vibrational structure in the 2n band. From calculations based on Franck-Condon factors, the authors conclude that on the graphite surface the equilibrium distance of the oxygen nuclei is decreased by 0.065 A relative to the gas phase. This would also be consistent with a partial electron withdrawal from oxygen antibonding orbitals into available orbitals in the graphite. 

The usually accepted approach is to adopt an ionic model for the superoxide ion on the surface. In this model, an electron is transferred from the surface to the oxygen to form 02, and there is an electrostatic interaction between the cation at the adsorption site and the superoxide ion. A calculation of the g tensor based on this model (Section 111,A,1) accounts for nearly all the data from adsorbed 02 and is consistent with the evidence that the spin density on both oxygen nuclei is the same (Section III,A,2). However, there are examples of oxygen adsorbed on the surface where the g values do not fit the predictions of the ionic model (Section IV,E) and also a few cases where the spin density on the two oxygen nuclei is found to be different. In these situations it seems likely that a covalent model in which a a bond is formed between the cation and the adsorbed oxygen, is more relevant. 

Selected 17 O Hyperfine Constants and Total Spin Densities for Diatomic Oxygen Species with Equivalent Oxygen Nuclei... 

So far, we have considered only those systems in which the two nuclei are equivalent. This is not the case for OJ on Mo03/Si02 (81, 82) and some y-irradiated zeolites (81, 83a), where the oxygen nuclei are found to be inequivalent. This case is considered in more detail in the next section. 

Fig. 7. The EPR specirum of 02 ion on MoO,/Si02 at 77 K showing the hyperfine interaction with two inequivalent oxygen nuclei (84).

Calculated using only Axx = A ( for inequivalent oxygen nuclei (see text) and assuming no motion is taking place. 

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