Divalent ions spectra

We must choose in the reversal of charge spectrum (p. 284, Fig. 14) a divalent ion which lies much further to the left if we want to obtain a distinct antagonism with gum arabic in a salt combination of the type (2 — 1) 4- (1 — 1). 

The cations of salt I are arranged in valency groups (the divalent in addition in subgroups), while within each division the order from top to bottom is that for increasing reversal of charge concentrations in the ion spectrum of egg lecithin (see p. 281, Fig. 10 p. 282, Fig. 12). This order is therefore that of decreasing affinity for the phosphate group. 

Membrane retentions to inorganic ions q>an the entire spectrum. Sodium chloride is used universally as a test solute, and membranes are available commercially with < 10% to >99% sodium chloride retention. Most other ions have higher retentions on a given membrane than does sodium chloride, and calcium, magnesium, sulfate, and other divalent ions always are retained to a much higher degree than is sodium chloride. 

A clear illustration of the resonance enhancement effect is shown in Figure 1 which depicts the spectra acquired for a 0.50 x 10 M solution of the familiar tris-phenanthroline (phen) complex of divalent ion plus 0.50 M sulfate ion as a nonenhanced internal standard. The complex possesses an intense metal-to-ligand charge transfer (MLCT) transition, centered near 510 nm. With 647.1 nm excitation, far to the red of the MLCT maximum, the acquired Raman spectrum is dominated by scattering from the sulfate ion, S04, whose symmetric j/(S—O) mode occurs at... 

The divalent rare-earth ion Eu has the 4f electronic configuration at the ground states and the 4f 5d electronic configuration at the excited states. The broadband absorption and luminescence of Eu are due to 4f - 4 f 5d transitions. The emission of Eu is very strongly dependent on the host lattice. It can vary from the ultraviolet to the red region of the electromagnetic spectrum. Furthermore, the 4f-5d transition of Eu decays relatively fast, less than a few microseconds [33]. 

When the pH is readjusted to a higher value, the splitting increases and a spectrum which is essentially the same as the one obtained originally at the higher pH is observed. However, when the pH of a sample solution is lowered from 12.7 down to 3.0, slow desorption of Co-57 ions was observed, and the Mossbauer spectrum virtually remained unchanged (Figure 3(F)). These observations suggest that the chemical form of divalent Co-57 adsorbed from an alkaline solution is retained when the pH of the solution is lowered down to an acidic pH value. 

In contrast to the case of divalent Co-57 ions described above, the spectra show no hysteresis against the lowering of pH. Conversely, the spectrum of a sample previously adjusted to a pH of 2.5 was found to remain broadened after the pH had been raised to 8.6 (Figure 5(F)). Thus, the chemical structure of pentavalent Sb-119 adsorbed from an acidic solution is considered to be retained when the pH of the solution is raised above 7. 

As a relevant example, Figure 6.4 shows the room temperature absorption spectrum of Eu + in sodium chloride (NaCl). In this crystal, europium is incorporated in the divalent state, replacing Na+ lattice ions. The spectrum of Eu + ion in NaCl consists of two broad bands, centered at about 240 nm and 340 nm, which correspond to transitions from the ground state ( 87/2) of the 4f electronic configuration to states of the 4f 5d excited electronic configuration. In fact, the energy separation between... 

The other end of the series, K3[Cr(NCS)e], has a spectrum with a pronounced preliminary peak at 16 ev., which peak increases in magnitude throughout the series in Fig. 18. The location of the peak might imply divalent chromium. However, from diffraction type arguments and the interpretation of the K3Co(CN)e spectrum of Fig. 13, this new peak introduced by the NCS group may be attributed to the Cr—C distances, i.e., to the second octahedral coordination sphere. As two and then four NCS ions are introduced into the coordination sphere, this preliminary peak is... 

In the lower panel of Fig. 10 we show the Sc 2p core-level photoemission spectrum of a UHV-prepared film of Sc2 C84 [34]. Analogous data, but from films prepared by dropping from a solvent solution in air, were used in [32] to argue that, as the binding energy of the Sc 2p spin-orbit split components is lower than in Sc203 (a trivalent Sc standard), the Sc ions in the endohedral fullerene are divalent. 

---