Lattice vibrations with electrons, 2251 table

Bulk crystalline radical ion salts and electron donor-electron acceptor charge transfer complexes have been shown to have room temperature d.c. conductivities up to 500 Scm-1 [457, 720, 721]. Tetrathiafiilvalene (TTF), tetraselenoful-valene (TST), and bis-ethyldithiotetrathiafulvalene (BEDT-TTF) have been the most commonly used electron donors, while tetracyano p-quinodimethane (TCNQ) and nickel 4,5-dimercapto-l,3-dithiol-2-thione Ni(dmit)2 have been the most commonly utilized electron acceptors (see Table 8). Metallic behavior in charge transfer complexes is believed to originate in the facile electron movements in the partially filled bands and in the interaction of the electrons with the vibrations of the atomic lattice (phonons). Lowering the temperature causes fewer lattice vibrations and increases the intermolecular orbital overlap and, hence, the conductivity. The good correlation obtained between the position of the maximum of the charge transfer absorption band (proportional to... 

An electron in a solid behaves as if its mass [CGS units are used in this review the exception is for the tabulation of effective masses, which are scaled by the mass of an electron (m0), and lattice constants and radii associated with trapped charges, which are expressed in angstroms (1A = 10 8 cm)] were different from that of an electron in free space (m0). This effective mass is determined by the band structure. The concept of an effective mass comes from electrical transport measurements in solids. If an electron s motion is fast compared to the lattice vibrations or relaxation, then the important quantity is the band effective mass (mb[eff]). If the electron moves more slowly (most cases of interest) and carries with it lattice distortions, then the (Frohlich) polaron effective mass (tnp[eff]) is appropriate [11]. The known band effective and polaron effective masses for electrons in the silver halides are listed in Table 1. The polaron and band effective masses are related to a... 

Probably the most important experimental work which confirms the cooperative nature of the spin crossover transition is the heat capacity measurements on Fe(phenanthroline)2(NCS)2 and Fe(phenanthroline)2-(NCSe)2 by Sorai Seki (1974). The variation in the molar heat capacity of the latter compound with temperature is shown in Figure 3.27. Not only does the heat capacity show a sharp peak at the transition temperature (see Table 3.9), but there is also a change in the heat capacity, for the two different spin states (see Figure 3.27) at the transition. These authors propose that the total heat capacity of each spin state is made up of contributions from lattice vibrations, intramolecular vibrations, and electron thermal excitation. From this they have determined the changes in enthalpy and entropy associated with the change in spin state at the crossover. The results of these calculations are given in Table 3.9 and they... 

The amount of high precision experimental structural data on conjugated polyenes is limited. Some structure results are presented in Table 5. In gas electron diffraction studies it is difficult to determine closely spaced bond distances accurately, because these parameters are highly correlated with the corresponding vibrational amplitudes. Today it is possible to calculate the vibrational amplitudes accurately, if the vibrational frequencies are known. This was, however, not the case when the GED studies presented in Table 5 were carried out. The observed differences between the terminal and central C=C bonds in the GED studies of traw.s-l,3,5-hexatriene and c/s-l,3,5-hexatricne are probably too large29. A very accurate X-ray study of traw.s-l,3,5-hexatriene has, however, been carried out also in connection with the preparation of this chapter4. Figure 4 shows the molecular structures of trans-1,3-butadiene and trans-l,3,5-hexatriene as found in the crystal lattice. 

Usually, however, the Bi3+ emission spectrum does not show vibrational structure at all, not even at 4.2 K. An outstanding example is B GejOi 2 [15]. It shows a broad-band emission with an enormous Stokes shift ( 2 eV). It is interesting to note that the Stokes shift of the Bi3+ emission varies from less than 1000 cm"1 (Cs2NaYCl6 Bi3+) to 20000 cm"1 (Bi2Ge309). This is illustrated in Table 2 [2], A large Stokes shift implies a high value of the electron-lattice... 

Distinct differences for the various matrices are observed with regard to the coupling of Pt(2-thpy)2 to lattice modes (phonons). These occur in the spectra as resolved phonon satellites and/or as umesolved phonon wings. Such satellites accompany all electronic transitions and also satelhtes of vibrational fundamentals. For example, in Tables 1,5, and 7 (shown later) energies of lattice mode satellites are given for n-octane. 

From a modest beginning with H-like atoms, to diatomic molecules, the field has now expanded to multidimensional problems. Here density functional theory is most appropriate, and initial studies have emerged (using nonorthonormal wavelets) [18]. Our abilities to calculate the electronic structure of multi-electron substances in cubic lattices [19] and molecular vibrations in four-atoms systems [20,21] have been extended by making full use of powerful parallel computers. The approach of Arias et al. [19] to determine the electronic structure of all the atoms in the periodic table is to expand functions, f, in three dimensions as a sum of scaling functions at the lowest resolution plus wavelet functions of all finer resolutions ... 

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