Ionization potentials, of the lanthanides

The Saha-Langmuir equation has been used to obtain both ionization potentials [25] and work functions [26]. Measuring ion beam intensities at several different temperatures and plotting their logarithms vs. 1/7" yield a straight line whose slope is ( - f)/k. If either or / is known, the other is readily calculated. Hertel introduced a method of measuring ionization potentials that was independent of the work function of the surface, using instead as reference an element of known ionization potential he applied it in the determination of the first ionization potentials of the lanthanide elements [27]. 

Discussion of Lanthanide Ionization Potentials. A summary of accurate ionization potentials of the lanthanides is given in the last two columns of Table III. For comparison, values from electron impact and the semi-emperical spectroscopic values are given in columns 2 and 3. Although their uncertainties are much larger, the agreement is quite good. 

Figure 9. Normalized ionization potentials of the lanthanides plotted as a function of number of f electrons. Only the cerium and gadolinium points required normalization to the 4P6s2 4fN6s + e process (3).

Figure 15. First (IPj) and second (IP2) ionization potentials of the lanthanide elements j La -2jLu. Experimental values are compared to results from 4f-in-core pseudopotential (PP) calculations with and without account of core-valence correlation effects by means of a core polarization potential (CPP) [95].

Figure 1 Klemm s graph of 1929/1930 (top) exhibiting lanthanide elements with stable di- and tetiavalent compounds a modem version of this graph for the divalent state is shown in the middle the difference AE° = E (Gd " /Gd ) -E (R +ZR ) is plotted to parallel Klemm s graph. Bottom The third ionization potentials of the lanthanides, I3 = AH° (3), in kJ mol ...

Tables 1.13a and 1.13b comprise the ground levels and ionization potentials of the neutral through triply ionized lanthanides (Martin et al., 1974).

The ionization potential of an element is one of its fundamental properties. It is known that the first ionization potential of heavy elements depends on relativistic effects. The Mainz group, in Germany, systematically determined the first ionization potential of the actinide elements from Ac through Es using laser spectroscopy as shown in Table 18.12 (Becke et al. 2002). O Figure 18.24 shows the comparison of ionization potentials between lanthanide and actinide atoms (Moore 1971 Becke et al. 2002). The atomic level structure of Fm (2.7 x 10 ° atoms) with a half-life of 20.1 h was studied for the first time by the method of resonance ionization spectroscopy. Two atomic levels were identified at wave numbers (25,099.8 0.2) cm and (25,111.8 0.2) cm (Sewtz et al. 2003). 

Culberson et al. (1987) used their INDO/1 method to investigate equilibrium structures and ionization potentials of selected lanthanide halides RX (n=2,3,4). The overall accuracy for bond lengths is usually better than 0.05 A, the values calculated for the... 

Differences in lanthanide and actinide hydration thermodynamics have been discussed by Bratsch and Lagowski (1986) who attributed the difierences to relativistic effects in the actinides which cause changes in the energies of the s, p, d, and f orbitals. For example, the first and second ionization potentials of the electrons of the 7s state of the actinides are higher than those of the 6s state of the lanthanides whereas the third ionization potentials are similar for both families and the fourth ionization potential is lower for the actinides than the lanthanides. The small decrease in IP3 and IP4 for the f configuration in the actinides results in smooth variations in the relative stabilities of the adjacent oxidation states across the actinide series while the greater spatial extension of the 5f orbitals increases the actinide susceptibility to environmental efiects (Johnson 1982). 

Although this seems to be rather confusing, there are, of course, reasons. The relative stabilities of the di-and bivalent states of the respective lanthanides throughout the series follow, more or less, the third ionization potentials of the elements, AH°(3) (Figure 1). With a standard electrode potential of °(Eu +/Eu +) = —0.35 V (which can be measured in aqueous solution), the ionization potentials or disproportionation enthalpies can be used to calculate standard electrode potentials °(R +/R +) for the whole series. This work has essentially been put forward by Johnson and These results may be summarized graphically... 

The role of bond ionicity in three-electron reactions is manifested in the reactions of lanthanide cations (Ln ) with R-F compounds which result in F abstraction and formation of LnF, as shown in equation (12). Here the promoted state which in covalent situations involves a triplet excitation of the molecule (Scheme 2) changes to a charge transfer state as 17 in Scheme 3. Thus, the finding of the Berlin group of an extended correlation between the efficiency of C-F bond activation by lanthanide cations and the second ionization potential of the metal cation is in line with an avoided crossing of ground and charge transfer states. ... 

In general, ionization potential decreases while going down the group. Therefore, ionization potential of the elments of second transition series have lower values than those of the elements of first transition series as expected. However, ionization potentials of the elements of third transition series except lanthanum have higher values of ionization potentials due to lanthanide contraction. The atomic radii of the elements of second and third transition series are almost same but atomic numbers differ by 32. Thus, the outer electrons are firmly attached to the nucleus and ionization potential values are very hi. On accoimt of this, the elements of third transition series are almost inert under ordinary conditions. 

Cerium is strongly electropositive having a low ionization potential for the removal of the three most weakly bound electrons. The trivalent cerous ion [18923-26-7] Ce ", apart from its possible oxidation to Ce(IV), closely resembles, the other trivalent lanthanides in behavior. 

In contrast to the lanthanide 4f transition series, for which the normal oxidation state is +3 in aqueous solution and in solid compounds, the actinide elements up to, and including, americium exhibit oxidation states from +3 to +7 (Table 1), although the common oxidation state of americium and the following elements is +3, as in the lanthanides, apart from nobelium (Z = 102), for which the +2 state appears to be very stable with respect to oxidation in aqueous solution, presumably because of a high ionization potential for the 5/14 No2+ ion. Discussions of the thermodynamic factors responsible for the stability of the tripositive actinide ions with respect to oxidation or reduction are available.1,2... 

Deviations from this rule may occur for elements to the right of the lanthanides in the periodic table. Here the nuclear charge has increased much more than in the previous row of the periodic table, because of the additional lanthanide elements, and the ionization potentials of many of these elements are in fact higher than the potentials of their family members in preceding rows of the periodic table (compare this to the lanthanide contraction, p. 52). 

Usually, the plot of Goldschmidt s ionic radii produced no inflection around the gadolinium region although Bommer 12) later supported Klemm s diad theory by plotting the cell constant (a) for the C-type lanthanide oxides. To support his diad theory Klemm has (13) also pointed out that while La(III) and Lu(III) possess empty (4 f°) and completely filled (4/14)/-shell respectively, Gd(III) has a half-filled shell (4/7), and that usually a break is observed around the half-filled shell. He plotted (13) the ionization potentials for the M - M+ reaction for the series B—Ne and Al-Ar and showed that a break does exist in the N—0 and P—S region. In Fig. 2 several plots are made using the newly acquired data (14). 

The ground terms and the ionization potentials (IP) for the processes in the case of the lanthanides are well documented (14). However, the thir ionization potentials... 

Ionization potentials of atoms are usually obtained by the determination of a photoionization threshold or more accurately by the observation of long Rydberg progressions. With the exception of a few of these elements with simple spectra, obtaining such measurements for lanthanides and actinides is difficult if not impossible by conventional spectroscopy. Therefore, very accurate ionization limits were not available for the majority of these elements.( 6)... 

The same arguments apply to the study of ionization thresholds. While some success has been possible for the elements with simpler electronic structure (ytterbium, europium, and thulium),(34>35) for the remainder of the lanthanides it is nearly an impossible task to unravel the spectra originating from the many populated metastable levels to accurately determine the ionization potential with confidence.(36)... 

We sincerely appreciate the contributions of our co-workers R. W. Solarz and J. A. Paisner in the determination of the lanthanide and uranium ionization potentials. 

Figure 22. Third (IP3) and fourth (IP4) ionization potential of Lanthanides 57 - 7jLu obtained with relativistic small-core energy-consistent PPs [254]. The four dashed lines for CASSCF/ACPF results correspond to basis sets including a subset of (16sl5pl2dl0f8g8h8i) up to f, g, h, and i functions. The solid line for CASSCF/ACPF results from these values as an 1 / -extrapolation to the basis set limit I - >.

Ground levels and ionization potentials for the neutral and singly ionized lanthanide atoms. The designation of the ground level of Tb 11 is enclosed in braces because the indicated level has not yet been experimentally established as lowest. , ... 

Place 15-mL sample tubes inside 50-mL holder tubes in the tube rack and replace the vacuum chamber cover, being sure that the tips are in the mouths of the 15-mL tubes. Add 1.9 mL of 1% H2SO4. Thru on the vacuum. When the samples are eluted into the tubes, turn off the vacuum and remove the cover. Add 100 pL 20 ppb Tm to each tube. Time approximately 10 min for 24 tubes. Tm is the second most rare of the lanthanides and is very close to U in ionization potential (6.19 V vs. 6.05 V). 

At a time when little was known about ionization potentials of lanthanide ions as well as about thermochemistry of non-tripositive lanthanide speeies, Johnson (1969a) showed that differences in the third ionization potentials /j of the lanthanides are primarily responsible for many of their apparent oxidation-reduction anomalies. In a subsequent paper (Johnson 1969b) he compared and contrasted the relative stabilities of the di-, tri- and tetrapositive oxidation states of the lanthanides and actinides, pointing out how much less is the change in ionization potential for actinides than lanthanides at the half-filled shell (see fig. 4). He elaborated (Johnson 1974) on the first paper by systematizing the properties of the dipositive lanthanide ions in conjunction with those of the alkaline-earth metal ions. 

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