Energies of Electronic States

Many of the systems of interest to the optical materials community, however, are based on host lattices that contain non-stoichiometric, doping ( 1 % or less) 

In the following sections, we consider theoretical and experimental aspects of the influence of pressure on electronic energies. We emphasize the two major effects, covalency and crystal field strength, that are responsible for determining electronic energies in transition metal and lanthanide systems. For convenience of discussion, we choose to treat covalency and crystal field effects separately and to describe each effect with an independent set of theoretical parameters. We note, however, that the separation of covalency and crystal field effects is only approximate and that each effect influences the parameter values of the other effect to some extent in most systems. Our discussion will focus on experimental variations of covalency (B, C and F ) and crystal field strength (Dq, B q) parameters with pressure and the predictions of the theoretical models that have been proposed to explain the variations. 

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Suppan P. (1990) Solvatochromic Shifts The Influence of the Medium on the Energy of Electronic States, /. Photochem. Photobiol. A50, 293-330. 

High pressure techniques, in contrast, offer a more powerful method for such studies. By applying pressure one can vary the interatomic distances continuously and thereby study the crystal structure dependence of the f-electron states directly. A second, equally interesting possibility is based on the different sensitivities of the energies of electronic states on interatomic distances. These specific sensitivities allows the experimentalist to alter the energy difference between two states and thus to get unique information about their mutual influence. 

Transition metal complexes (TMCs) represent another, somewhat better known, Holy Grail of the semiempirical theory. The HFR-based semiempirical methods and the DFT-based methods suffer from structure deficiency, which does not allow it to reproduce relative energies of electronic states of different spin multiplicity within their respective frameworks without serious ad hoc assumptions. 

Table 11. Energies of electronic states [cm emission decay and spin-lattice relaxation times of triplet sublevels (I, II, and III) at T< 3 K. The compounds are arranged according to an increasing value of the total zero-field splitting AEjnj...

Fig. 29.— Relationship between various processes used to obtain information on energies of electronic states in a defect ionic solid.

The UV-VIS radiation gives rise to changes in the energy of electronic states of a molecule. The probability of electronic transitions in a molecule depends on the presence of multiple bonds in the molecule and on the kind, number and positions of the substituent groups. Determination of the kind of transitions corresponding to the observed bands of absorption spectra enables one to determine the structure of the molecule. 

Accordingly, we discuss below the MDOS as structure induced as proposed by several authors [5.18,28,30-33]. The large dots in Fig. 5.15 indicate binding energies of electronic states at the pseudo Brillouin-zone boundary, roughly estimated with the E versus k relation of free electrons... 

Fig. 3 TS-type diagrams correlating the energies of electronic states in d2 and S oxo-metal complexes with the strength of the An ligand field splitting parameter. Gray areas correspond to forbidden An zones for ground-state complexes...

The e (KE) peaks in the PES (fixed hu) provide information about the relative energies of electronic states of the AB neutral molecule (for example AsO-, Lippa et al., 1998) that, owing to spin or orbital selection rules, are not easily observed by direct study of the neutral molecule spectrum. An anion photodetachment spectrum is recorded by detecting the low-energy electrons ejected as the photon energy is scanned through the successive photodetachment thresholds associated with the energies of each neutral molecule rovibronic state. 

Prabhumirashi and Kunte [181] have proposed a new procedure employing Bakhshiev s equation for solvatochromic frequency shifts for excited-state dipole moments and specific solute -solvent interaction energies based on absorption spectra only, without using emission spectra. Suppan [182] has expanded upon the solvatochromic shift method and discussed the effect of the medium on the energies of electronic states and Ghoneim and Suppan [183] discussed solvatochromic shifts of non-dipolar molecules in polar solvents. 

Figure 11.3 is an example of a correlation diagram for the configuration cf. These diagrams illustrate how the energies of electronic states change between two extremes ... 

Suppan, P. Solvatochromic shifts The influence of the medium on the energy of electronic states. J. Photochem. Photobiol.. A Chem. 1990. 50. 293-330. 

It is useful to represent the energies of electronic states and the processes that interconvert them with a Jablonski diagram (Figure 12.6). ° The vertical scale represents potential energy. The horizontal scale has no particular significance it merely allows us to separate the sets of energy levels for the singlet... 

Experimental data on the ir-accepting ability of alkylphosphines are ambiguous. Photoelectron spectroscopy indicates that aliphatic phosphines are poor Tr-acceptors, ° but one study on a complex with an electron-rich (P metal center suggested that the relative energies of electronic states could be influenced by rr-back-donation into the cr-bonding orbitals of an aliphatic phosphine. The NBO analysis concluded that alkylphosphines are effective ir-acids. Tlius, further debate is likely to ensue about the ir-accepting ability of alkylphosphines, but other phosphorus ligands are clearly ir-acceptors. 

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