Spin neodymium

A major advance in the investigation of the intramolecular dynamics of spin equilibria was the development of the Raman laser temperature-jump technique (43). This uses the power of a laser to heat a solution within the time of the laser pulse width. If the relaxation time of the spin equilibrium is longer than this pulse width the dynamics of the equilibrium can be observed spectroscopically. At the time of its development only two lasers had sufficient power to cause an adequate temperature rise, the ruby laser at 694 nm and the neodymium laser at 1060 nm. Neither of these wavelengths is absorbed by solvents. Various methods were used in attempts to absorb the laser power, with partial success for microsecond relaxation times. 

The 3d levels in lanthanides are far removed from 4f levels and the overlap of these two levels if any is very small. As a result, multiplet structure in the 3d region is not expected. Although this is the case, XPS of some lanthanide compounds, particularly elements from lanthanum to neodymium, exhibit splitting in the bands apart from the doublet due to spin-orbit interaction. This type of structure is shown in Figs. 9.10, 9.11 and 9.12. These splittings are known as satellites and originate from multielectronic excitations. In general,... 

Another difference is that the 5/orbitals have a greater spatial extension relative to the Is and Ip orbitals than the 4/orbitals have relative to the 6s and 6p orbitals. The greater spatial extension of the 5/orbitals has been shown experimentally the esr spectrum of UF3 in a CaF2 lattice shows structure attributable to the interaction of fluorine nuclei with the electron spin of the U3+ ion. This implies a small overlap of 5/ orbitals with fluorine and constitutes an / covalent contribution to the ionic bonding. With the neodymium ion a similar effect is not observed. Because they occupy inner orbitals, the 4/ electrons in the lanthanides are not accessible for... 

TABLE 10 The magnetic properties of neodymium on a variety of crystal lattices (fee, bee, simple cubic, and hexagonal lattices) calculated as described in the text. The magnetic moments are all written in units of the Bohr magneton. The second column is the spin magnetic moment of the valence s, p, d, and f-states. The third column is the orbital moment associated with the valence electrons. The final two columns are the spin and orbital magnetic moments of the Sl-coirected f-states... 

Now let us consider the effect of crystal environment on the magnetic moment of the lanthanides. In Table 10, we show the results of calculations of the magnetic moment of neodymium on several common crystal lattices. A trivalent Nd ion yields a spin moment of 3/lb and an orbital moment of 6/ib- In the final two columns of Table 10, we see that the SIC-LSD theory yields values slightly less than, but very close to, these numbers. This is independent of the crystal structure. The valence electron polarization varies markedly between different crystal structures from 0.34/ib on the fee structure to 0.90/Zb on the simple cubic structure. It is not at all surprising that the valence electron moments can differ so strongly between different crystal structures. The importance of symmetry in electronic structure calculations cannot be overestimated. Eor example, the hep lattice does not have a centre of inversion symmetry and this allows states with different parity to hybridize, so direct f-d hybridization is allowed. However, symmetry considerations forbid f-d hybridization in the cubic structures. Such differences in the way the valence electrons interact with the f-states will undoubtedly lead to strong variations in the valence band moments. 

In a temperature-jump study using a pulsed neodymium laser, Creutz and Sutin were able to study the interconversion between the low-spin planar CAig) and high-spin octahedral CA g) forms of the nickel(ii) complex of (17). The relaxation time was 0.30 ps at 23 °C and was, as expected, independent of the concentration of the complex. 

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