Electronic transitions classifications

CLASSIFICATION OF MOLECULAR ELECTRONIC TRANSITIONS AND EXCITED STATES... 

Examples of this class of enzymes are glucose oxidase and D-amino acid oxidase The classification of the flavoproteins used here is that originally suggested which has been modified recently . In the author s own view the original classification has the advantage of being simple and yet quite useful whereas the new classification does not add to simplify and classify the rather complex picture of flavoprotein catalysis. Nevertheless, in flavoprotein oxidases, the 1,5-dihydroflavin is very reactive towards Oj. On the other hand, the two-electron reduced form of flavoprotein oxidases reacts slowly with pure one-electron acceptors, e.g. ferricyanide. That the two-electron transition is biologically favoured in these enzymes explains why they can react easily with sulfite... 

Electronic transitions are usually divided into two groups permitted and forbidden. However, such grouping is rather relative. Sometimes El-transitions are called permitted, whereas all the rest are considered as forbidden. More exact and general is classification of transitions satisfying the above-mentioned selection rules as permitted. Otherwise, if at least one selection rule is violated, the appropriate transition is called forbidden. 

B. Vibrational Structure of Electronic Transitions 1. Normal vibrations and their symmetry classification An electronic band system belonging to a polyatomic molecule normally contains a large number and variety of transitions in which vibrational quantum changes are superimposed on the electronic jump. The analysis, besides supplementing infrared and Raman evidence of the ground state frequencies, yields values for the fundamental frequencies of the excited state and is one of the principal sources of information as to its structure. 

Electroinidated polymerization is induced by electron transitions between the electrodes and the molecules of the electrolyzed solution. The following classification is based on the features of the transfer reaction [309]. 

For the sake of simplicity, electronic transitions in metal complexes are usually classified on the basis of the predominant localization, on the metal or on the ligand(s), of the molecular orbitals involved in the transition (4). This assumption leads to the well-known classification of the electronic excited states of metal complexes into three types, namely, metal-centered (MC), ligand-centered (LC), and charge-transfer (CT). The CT excited states can be further classified as ligand-to-metal charge-transfer (LMCT) and metal-to-ligand charge-transfer (MLCT). 

Following Jorgensen classification (ref.6) and our own previous considerations (ref.4,5), the electronic transition with ligand to metal charge transfer character involving isolated framework Ti (IV) in tetrahedral coordination is expected at 48,000 cm , while that involving isolated Ti (IV) in octahe-... 

In terms of this sort of classification, electronic transitions can be of five types (a) ligand-based transitions, (b) metal-based transitions, (c) metal-to-ligand transitions, (d) ligand-to-metal transitions and (e) inter-valence transitions. These will be considered in turn in the following sections. 

Though the classification of the electronic transitions of the DNA macromolecule according to Tt-type or lone-pair states of the monomers is only approximate, it is still possible to assign the exciton bands to monomer levels if the Wannier functions are contracted to molecular orbitals. As observed also in previous ab initio calculations on nucleotide bases and polynucleotides, the n and lone-pair levels are always mixed. In our case, for the three highest filled and three lowest unfilled bands, respectively, the ordering n, n, n, n, n, n has been found. The first two singlet monomer excitation energies obtained at 5.04 and 6.07 eV, respectively, must be compared with the experimentally observed values of 4.5 and 5.2 eV. 

It is often convenient, as it is now, to divide the fundamental ways in which color is created in chemical substances into two classes corresponding to the traditional division into organic and inorganic compounds. However, it wiU become apparent later in the discussion that this division is not a strict one since some compounds in both classifications exhibit color by the same type of mechanism. In aU cases, electronic transitions between energy level differences in the visible region of the spectrum must take place. 

---