Orbital quenching

These are summarized together with previous results [4] in Table 1. It is seen from Table 1 that the total moment of each compound is controlled by the orbital moment. Although the magnetic moment increases with going down from X = Se to Te, the absolute value of spin moment decreases while that of orbital moment changes little. These results imply that some orbital quenching happens to occur due to f-d hybridization between U atoms and/or f-p hybridization between U atom and chalcogenide atom. 

Figure 28. Energy-transfer spectrum for C2H4, resembling 3p orbital quenching by diatomic molecule.

In describing the magneto-optical properties one has to take account of the spin-orbit splitting, which was not included in the band-structure calculations of de Groot et al. These authors note that no orbital quenching occurs at the F point in the Brillouin zone so that here one may expect the spin-orbit interaction to be a maximum. It follows from the magneto-optical spectra that the onset of the Kerr peak at about 2 eV is located near 1 eV (see fig. 37). From these considerations it follows that the transition responsible for the large Kerr intensity involves initial electron states located rather close to the top of the valence band (at F in the lower... 

The complex Os(bpy)3 has an excited state lifetime of 19 ns in aqueous solution and excited state potentials of -0.96 V and 0.59 V for (M /M ) and E (M /M"), respectively. This excited state lifetime is considerably shorter than that of Ru(bpy)3, which is to be expected on the basis of spin-orbit quenching and from the excited state redox potentials—Os(bpy)3 is a stronger reductant but a weaker oxidant than is Ru(bpy)3. When one or more of the bpy ligands are substituted by ligands L, systematic changes in the excited state energies and lifetimes can be induced as has been done for the ruthenium analogues. ... 

Optical recording systems, 6, 126 Optical resolution amine metal complexes, 2,25 Oral contraceptives iron deficiency, 6, 764 Orbital angular momentum quenching, 1,262 /-Orbital systems... 

The problem could be stated from another point of view. In an isostructural series the uranium and neptunium compounds tend to be itinerant electron magnets or band magnets (like iron) and their orbital contribution is at least partially quenched. For much heavier actinides we know that the compounds will make local moment magnets with orbital contributions. It is quite possible that in between these two clear cut forms of magnetism that the intermediate case could be dominated by fluctuations, and no recognizable form of magnetism would occur. To state that the... 

On account of the quenching of the orbital mechanical and magnetic moment of atoms on bond formation, all electron-pair-bond complexes are to he represented as 27 states. 

The values for the atomic saturation magnetization at the absolute zero, ferromagnetic metals iron, cobalt, and nickel are 2.22, 1.71, and 0.61 Bohr magnetons per atom, respectively.9 These numbers are the average numbers of unpaired electron spins in the metals (the approximation of the g factor to 2 found in gyromagnetic experiments shows that the orbital moment is nearly completely quenched, as in complex ions containing the transition elements). 

Fluorimetric methods of analysis make use of the natural fluorescence of the analyte, the formation of a fluorescent derivative or the quenching of the fluorescence of a suitable compound by the analyte. Fluorescence cannot occur unless there is light absorption, so that all fluorescent molecules absorb, but the reverse is not true only a small fraction of all absorbing compounds exhibits fluorescence. The types of molecule most likely to show useful fluorescence are those with delocalised ji-orbital systems. Often, the more rigid the molecule the stronger the fluorescence intensity. Naturally fluorescent compounds include Vitamin A, E (tocopherol). 

The stereochemistry of dienes has been found to have a pronounced effect in the concerted cyclo-additions with benzyne 64>65h A concerted disrotatory cyclo-addition of tetrafluorobenzyne, leading for example with trans- (3-methylstyrene to (63, R = Me), is likely and in accord with the conservation of orbital symmetry 68>. However while the electro-cyclic rearrangement of (63, R = H) to (65, R = H) is not allowed, base catalysed prototropic rearrangement is possible. A carbanion (64, R = H) cannot have more than a transient existence in the reaction of tetrafluorobenzyne with styrene because no deuterium incorporation in (65) was detected when either the reaction mixture was quenched with deuterium oxide or when the reaction was conducted in the presence of a ten molar excess of deuteriopentafluorobenzene. 

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