Excited species electron configurations

Figure 5.37. Ground- and excited-state electronic configurations of [Fe(C5Me5)2] and TCNE species. Adapted from Miller, J. S. Calabrese, J. C. Rommelmann, H. Chittipeddi, S. R. Zhang, J. H. Reiff, W. M. Epstein, A. J. J. Am. Chem. Soc., 1987,109, 769. Copyright 1987 American Chemical Society.

Almost all Raman spectra of adsorbed species have therefore relied on enhancement effects. Thus, if the incident radiation can simultaneously excite an electronic absorption (see Figure 2.52), then the polarisabilily change associated with this change in the electronic configuration is very large. The... 

Holten and coworkers have also shown that 4-coordinate Ni-porphyrin species existing in coordinating solvents are induced to pick up ligands by laser excitation (45-47). This ligand-uptake process can also be understood in terms of the d-electron configuration of the metal. For the Ni-porphyrin molecules that have no axial ligands, the (d 2 ) state is the groun state. 

The direct product is also useful for determining the symmetry of ip9l from the symmetry of the occupied MOs. For two nonequivalent electrons outside closed subshells, the symmetry species of el is given by the direct product of the species of the orbitals of the two electrons. For example, the first excited electronic configuration of H20 is... 

If the ir - 77 transition leads to a non-planar structure the first excited electron configuration (31), in which the excited states are labelled by the D2h species classification,... 

Vibrationally equilibrated electronic excited states in molecules are unique chemical species. These are metastable species with unusual electronic configurations, and on this basis alone they might be expected to exhibit unusual patterns of reactivity. However, it is probably a more striking feature... 

The starting point for the analyses of the various electronic spectra and the corresponding photophysical decay processes begins with a consideration of the electronic states and the electronic configurations in the excitation processes. A schematic view of the molecular orbitals [6] is given in Figure 2.2, along with the symmetry species of the individual orbitals and their approximate descriptions. 

A quencher should have an excitation energy lower than that of the donor species and the appropriate electronic configuration. Transfer of excitation energy proceeds by radiative or radiationless deactivation of the donor molecular entity. Radiative energy transfer (also called trivial energy transfer) consists of light emission by the donor molecule and reabsorption of the emitted light by the acceptor molecular entity. 

Since photochemistry is essentially the study of electronically excited species, it is now necessary to see how light can alter the electronic configuration in an absorbing species, or how a change in the configuration can lead to emission of light. 

Fig. 6.2 Activation of triplet molecular oxygen ( 02) by electronic excitation or by consecutive one-electron reductions and the corresponding electron configurations of the resulting reactive oxygen species.

---