State, electronic derivation from configuration

The spectrum of singly ionized europium (Eu+, EuII). — The seceond spectrum of europium (Eu II) has been measured by Russell et al. [487]. The ground state is derived from the addition of an electron to the parent core and is found to have the configuration 4/7(8 7/2)6p. They have in particular identified 156 levels originating from to the coupling of a 6s, 6p or 5d electron with the 4/7(8 7/2) core. The lowest terms are 9S and 7S. 

Biphenylene and trisdehydro[12]annulene are representatives of conjugated hydrocarbons with a 4 -membered ring. The pattern of their absorption spectra is completely different from that of benzenoid aromatics. Their HOMO and LUMO are derived from the two NBMOs of an ideal perimeter and both the lowest excited singlet and triplet state can be described by the configuration A ho lu- The transition is symmetry forbidden in molecules of D2h symmetry or higher. Nonradiative decay usually dominates their photophysical properties. Quantum yields of fluorescence and intersystem crossing are low.307 The LCAO version of Platt s perimeter model has been extended to treat conjugated systems with AN jt-electrons derived from [ ]annulenes.308,309... 

Reexamine the development of the electronic-state function, derived from the lowest excited configuration of benzene, using a set of functions in the complex basis X iy, X — iy icf. Example 7.3). 

Derive the states which arise from the following electron configurations ... 

The single-electron crystal-field picture may be a crude over-simplification because Coulomb repulsion and SOC can lead to a situation where the ground term is a composite mixture of = 1/2, 3/2, and 5/2 states that does not derive from a single configuration [71, 72] the corresponding physical description is obtained from proper quantum chemical calculations [73-75]. 

In contrast, it is accepted practice that referring to, for example, an iron(III) complex implies that this compound contains an iron ion with a high-, intermediate-, or low-spin electron configuration. Since n for a d" configuration is, at least in principle, a measurable quantity, it has been suggested [3] that an oxidation number n, which is derived from a known d configuration, should be specified as physical or spectroscopic oxidation number (state) [4—6]. 

In complex organic molecules calculations of the geometry of excited states and hence predictions of chemiluminescent reactions are very difficult however, as is well known, in polycyclic aromatic hydrocarbons there are relatively small differences in the configurations of the ground state and the excited state. Moreover, the chemiluminescence produced by the reaction of aromatic hydrocarbon radical anions and radical cations is due to simple one-electron transfer reactions, especially in cases where both radical ions are derived from the same aromatic hydrocarbon, as in the reaction between 9.10-diphenyl anthracene radical cation and anion. More complex are radical ion chemiluminescence reactions involving radical ions of different parent compounds, such as the couple naphthalene radical anion/Wurster s blue (see Section VIII. B.). 

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