Lanthanide spectroscopic constants

It is neither intended nor possible to give a comprehensive review of relativistic density functional calculations on small molecules. To be able to compare the methods described in Sec. 2, we will primarily discuss molecules for which computational results from a variety of different methods are aveulable. Molecules containing heavy elements from the left half of the periodic table (including lanthanides and actinides) will not be discussed, as most of this is covered in the eirti-cle by V. Pershina in this volume. Likewise, only calculations of molecular spectroscopic constants such as bond lengths (r ), (harmonic) vibrational frequencies ((0 ) and binding energies (D ) are... 

Spectroscopic constants [Re( )> ( V)] of lanthanide hydrides at various levels of theory. Reproduced from... 

A study of the monohydrides, monoxides, and monofluorides of lanthanides and actinides using ab initio all-electron and pseudopotential techniques is also available. The spectroscopic constants of low-lying electronic states of ThO " ... 

Preuss, Stoll, and co-workers at Stuttgart have employed several other ECP methods, which include core polarization effects in molecular calculations. The ECPs for all of the elements in the periodic table including lanthanides and actinides have been generated by these authors. They have also used these ECPs for computing the spectroscopic constants and potential energy curves of lanthanide oxides such as GdO, EuO, YbO, etc. 

TRES appears to be a sensitive tool to follow lanthanide and actinide complexation in solution, because most of the spectroscopic parameters are influenced by complexation. It has been shown that caution should be paid to the type of photochemical processes occurring in solution in order to correctly analyse the data. Taking account this important point, TRES is an interesting technique for the determination of equilibrium constants. From a more fundamental viewpoint, one may wonder why inorganic ligands lead to regime A with U(VI) and to regime C with Cm(III). 

In the lanthanide series, we have 14 elements that result from the addition of electrons into the f orbitals. For the lanthanide series, the electron configurations are 4f (1—14). In the lanthanide series, the majority of the compounds are formed by trivalent M3+ ions. From a spectroscopic point of view, all the rare earth ions have a large spin-orbit coupling constants, resulting in electronic states being defined by the angular momentum... 

The enhancement of the extraction of Ln(III) ions with ttfaH in cyclohexane or benzene by the addition of Cr(acac)3 was investigated . The equilibrium analysis suggested that the effect of Cr(acac)3 could be ascribed to the formation of a binuclear 1 1 La(ttfa)3-Cr(acac)3 adduct. The formation constants of adducts along the lanthanide series decreased with the decrease of the ionic radii among the light lanthanides and were constant for their heavy counterparts. UVV, IR and H NMR spectroscopic studies were also performed to explain the molecular structural differences between the light and heavy lanthanide complexes. 

Besides these discrepancies between crystallographic results and the instantaneous evidence obtained by spectroscopic measurements, there occurs another interesting discrepancy between classical physico-chemical and spectroscopic investigations. A very characteristic case is that of normal anion complexes and the outer-sphere ion-pairs in solution. This distinction is clear-cut in stable complexes (23) such as [Cr(H20)6]" S04 and [Cr(S04)(H20)4 or In the case of lanthanide chlorides, it is well-known that spectroscopic evidence (42, 75) for inner-shell complexes NdCl(H20)x indicates a formation constant hundreds of times smaller than that of the ion pair Nd(H20)g+ Cl . In organic solvents the inner complexes are relatively more abundant (2, 43). In certain cases, one also... 

Figure 8 Simplified Jablonski diagram showing the sensitization pathway from the chromophoric hgand L to the lanthanide ion Ln " via the triplet state T of the sensitizer. The k values are the rate constants for aU photophysical phenomena involved. Absorption by the sensitizer, intersystem crossing kisc of the sensitizer, and energy transfer k from the triplet state of the sensitizer to the lanthanide ion (to one of its excited spectroscopic level) resulting in an...

The lanthanide compoimds imder consideration have a large number of excited electronic states (Kaledin et al., 1996a), which complicates the interpretation of spectroscopic data. In particular, the molecular constants for the groimd state cannot be always determined. The available data should be preliminarily tested for reliability, and missing data should be completed. To this end, a semiempirical approach is possible in which the results are checked for correspondence with the known principle of the change in a given parameter in a series of related compoimds. 

---