Interaction charge transfer systems

Schematic diagrams appropriate to NMP/TCNQ and TTF/TCNQ are shown in Fig. 30 and are based on experimental studies. Application of the one-dimensional Hubbard model to analyse low and high temperature data for NMP/TCNQ yielded consistent values of U and t. For TTF/TCNQ and HMTSF/TCNQ, the increased cation polarizability is believed to have successfully reduced the strength of the effective electron-electron interaction with the result that a true metal-semiconductor transition is observed at 58 K for TTF/TCNQ which disappears completely for HMTSF/TCNQ. At present the advantages of using complex salts as against simple salts of charge-transfer systems to produce organic metals are not clear, particularly since the...

For [Li C6o]" the calculated (hyper)polarizabilities are roughly comparable to those of the hypothetical non-interacting system obtained by charge transfer of the Li valence electron to the cage giving Li+ + Ceo. The same is true for the linear polarizability of the neutral but the non-interacting charge transfer model completely breaks down for the hyperpolarizabilities. 

Chemisorption occurs when the attractive potential well is large so that upon adsorption a strong chemical bond to a surface is fonued. Chemisorption involves changes to both the molecule and surface electronic states. For example, when oxygen adsorbs onto a metal surface, a partially ionic bond is created as charge transfers from the substrate to the oxygen atom. Other chemisorbed species interact in a more covalent maimer by sharing electrons, but this still involves perturbations to the electronic system. 

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