Divalent energy levels

The HOMO and HOMO-1 orbitals of the carbodicarbenes 6 and 7 also have the largest coefficients at the divalent C(0) atom (Fig. 4) but the 7i-type HOMO exhibits some delocalization in the NHC ring (Fig. 4). The energy levels of the frontier... 

Fig. 5.3. The energy levels scheme of the free divalent lanthanides. The solid curve (a) connects the locations of the first 4/" 5d level (Dorenbos 2003)...

Divalent vanadium belongs to 3d ions and is isoelectronic with Cr. Hence all energy levels and spectral characteristics are similar. The difference between them lies in the lower crystal field strength for V in comparison with Cr. ... 

Platinum porphyrin complexes can be prepared by reaction with PtCl2(PhCN)2. Purification of the final complex is by medium pressure liquid chromatography on alumina. The strongly phosphorescent platinum(II) porphyrin complexes are efficient sensitizers for stilbene isomerization. The quantum yields for the cis to trans process are greater than unity because of a quantum chain process in which the metalloporphyrin serves both as an energy donor and an acceptor.1110 Picosecond laser spectroscopy has been used to obtain time-resolved excited-state spectra of platinum octaethylporphyrin complexes, and to probe the excited-state energy levels.1111 Tetrabenzoporphyrin complexes have been prepared for platinum in both the divalent and tetravalent oxidation states. The divalent complex shows strong phosphorescence at 745 nm.1112... 

A. Mn(II) EPR. The five unpaired 3d electrons and the relatively long electron spin relaxation time of the divalent manganese ion result in readily observable EPR spectra for Mn2+ solutions at room temperature. The Mn2+ (S = 5/2) ion exhibits six possible spin-energy levels when placed in an external magnetic field. These six levels correspond to the six values of the electron spin quantum number, Ms, which has the values 5/2, 3/2, 1/2, -1/2, -3/2 and -5/2. The manganese nucleus has a nuclear spin quantum number of 5/2, which splits each electronic fine structure transition into six components. Under these conditions the selection rules for allowed EPR transitions are AMS = + 1, Amj = 0 (where Ms and mj are the electron and nuclear spin quantum numbers) resulting in 30 allowed transitions. The spin Hamiltonian describing such a system is... 

The procedure for calculating energy level diagrams by the self-consistent field Xa scattered wave (SCF-Xa-SW) method is as follows (Sherman, 1984, 1991). An octahedral cluster such as [FeO6]10 is partitioned into a set of (overlapping) spheres centred about divalent iron and each oxygen atom, and these are surrounded by an outer sphere. Within each atomic sphere the one-electron Schrodinger equation... 

Figure 11.6 Molecular orbital energy level diagrams computed for iron octahedrally coordinated to oxygen. Left divalent iron in the [Fe06]-1° cluster (based on Sherman, 1991) right trivalent iron in the [Fe06]-9 cluster (from Sherman, 1985a). Orbital energies have been scaled relative to zero for the non-bonding 6rlu level.

Fig. 1.4. Energy levels and occupancies (red) of the MOs at the divalent C atom of linear carbenium ions =C —R (left) and bent carbanions =Ce—R (right). The indices of each of the four MOs refer to the AOs from the central C atom.

Fig. 1.3. Energy levels and occupancies (red) of the MOs at the divalent C atom of linear carbenium...

Divalent Ions. The 4fn and 4fn 5d energy levels of divalent lanthanides have been studied in alkaline-earth fluoride crystals (86, 87). The 5d levels occur at lower energies than for the isoelectronic trivalent state and in most cases extend into the visible. Because the spin-orbit parameters are smaller for the divalent ions, the separations of the J states of the 4fn configuration are reduced. 

Laser action has been reported for three divalent lanthanides (2J, 34). Figure 6 summarizes the energy levels, transitions, and approximate wavelengths of these lasers. Only crystals have been used as hosts and reduced temperatures were used in all cases. 

Figure 6. Energy levels and laser transitions for divalent lanthanide ions. Approximate wavelengths of transitions are given in micrometers.

Table II. The Highest Occupied Electronic Energy Levels (in eV) of the Monomeric Divalent Metal Alkyls and Dialkylamides...

The divalent titanium ion, Ti ", in TiO has two 3d electrons and so the metal d band shown in Figure 30.6 is partially filled. It is this partially filled band, which you will notice resembles the energy level diagram for a metal shown in Figure 30.2, that leads to metallic conductivity in TiO. Looking at Figure 30.6 it is easy to see why titanium dioxide, Ti02, is an insulator. In the formation of the Ti" " ion, both the two 4s electrons... 

Fig. 1.6 Position of the 4f state of divalent lanthanide ions in CaGa2S4. m is the numbca- of 4f" electron, and E is the Fermi energy level. Reprinted with the permission from Ref. [25]. Copyright 2005 American Chemical Society...

Fig. 4.13 Energy-level scheme of divalent and trivalent lanthanides in Cap2. Energies corresponding to Ln and Ln " are indicated by blue dashed lines and red solid lines, respectively. The lowest states of 4f electronic configurations are re nesented by triangles. Possible 4f 5d — 4f transitions are indicated by vertical arrows. Reprinted from Ref. [153], copyright 2004, with permission fiom Elsevier...

In a vast majority of these applications, these ions are introduced into crystalline solids in their stable trivalent state. However, there are a few lanthanide ions whose divalent state is also stable, e.g., Eu ", Tm ". One of the main differences between the trivalent and divalent lanthanides (apart from the electrical charge) is that the charge-transfer transitions and the parity allowed 5d-4f transitions of the divalent ions are located at lower energies than those of the trivalent ions because of this they can more easily studied experimentally. Regarding Tm " ions, it should be kept in mind that the 4f electron shell has only two energy levels the ground state p7/2 and the excited state located at approximately 9500 cm [2]. As a result, the 4f-4f and 4f-5d transitions of the Tm ions do not overlap and can be easily studied separately. 

Kiss ZJ (1962) Energy levels of divalent thulium in CaF2. Phys Rev 127 718... 

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