Energy different electronic states

The second and third energy terms in equation (1) could be interchanged without any effect (i.e. it is impossible to say which electron fills the initial core hole and which is ejected as an Auger electron they are indistinguishable. The existence of different electronic states within the final doubly ionized atom may furthermore lead to fine structure in high-resolution spectra. 

Fluorescence is a process that occurs after excitation of a molecule with light. It involves transitions of the outermost electrons between different electronic states of the molecule, resulting in emission of a photon of lower energy than the previously absorbed photon. This is represented in the Jablonski diagram (see Fig. 6.1). As every molecule has different energy levels, the fluorescent properties vary from one fluorophore to the other. The main characteristics of a fluorescent dye are absorption and emission wavelengths, extinction... 

The radiationless transition between two states of same spin is called internal conversion, the one occuring with inversion of spin being termed intersystem crossing. In both processes the excess energy is liberated as heat. All these transitions between different electronic states are customarily preceded by vibrational relaxation, i.e. the deactivation from a higher vibronie level to the v0-level of the same electronic state (Fig. 5). 

Unfortunately, the dynamic correlation energy is not constant for a given molecule but may vary considerably between different electronic states. Thus, any procedure geared towards quantitative accuracy in predicting excited-state energies must in some way account for these variations. The most economical way to achieve this is to introduce a number of parameters into the model. By scaling those to a set of experimental data... 

Transitions between different electronic states result in absorption of energy in the ultraviolet, visible and, for many transition metal complexes, the near infrared region of the electromagnetic spectrum. Spectroscopic methods that probe these electronic transitions can, in favourable conditions, provide detailed information on the electronic and magnetic properties of both the metal ion and its ligands. 

Comparison is made to experimental energies that have been averaged over the J quantum number. This works well for the first row atoms where the spin-orbit coupling is small and there is little interaction between different electronic states but becomes more questionable for the second and third row atoms. We shall return to this problem later. 

Infrared spectroscopical data encode a lot of structural information and can be analyzed with the help of computational methods (vide supra) aiding in the identification of the observed species. Sometimes, two different electronic states may lie very close in energy and have similar geometries. In such cases (e.g., the quinonoid radicals to be described in Section II.B.), the predicted differences in the IR spectra are too small to allow an unambiguous assignment of the ground-state multiplicity. In this respect, ESR spectroscopy provides valuable comple-... 

Finally the valence-bond depictions of Fig. 3, although not perfect, seem to be useful intuition guides in the study of these systems and reasonable approximations to estimating the relative energies of the different electronic states. 

A thermal oxidation of 2,3-dimethyl-2-butene, 16, occurs in NaY when the temperature of the oxygen-loaded zeolite in raised above — 20°C [35], Similar thermally initiated oxidations were not observed for the less electron rich tram-or cix-2-butene. Remarkably, pinacolone was conclusively identified as one of the products of the reaction of 16, This ketone is not a product of the photochemical Frei oxidation (vide supra) and underscores the very different character of these two reactions and the complexity of the oxygen/16 potential energy surface, A rationale for the different behavior could lie in the different electronic states of the reactive oxygen-CT complex in the thermal and photochemical reactions. Irradiation could produce an excited triplet-state CT complex ( [16 O2] ) and/ or ion pair ( [16 02 ] ) with different accessible reaction channels than those available to a vibrationally excited ground-state triplet complex ( [16 "02]) and/... 

The main decay processes to the ground state shown in Figure 4.1, which is essentially an energy diagram for the different electronic states, are ... 

When two (or more) potential energy surfaces corresponding to different electronic states of a chemical system are close to one another in energy, the electronic wave function should really be written as a linear combination of the different adiabatic wave functions. For simplicity, let us consider the case of only two states, in which case we would write... 

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