Electron-molecular vibration coupling

Coherence (transition efficiency) depends on the degree of electron-phonon or electron-molecular vibration coupling. 

The first two terms describe, respectively, the radical electrons and the molecular vibrations in the absence of vibronic coupling. Linear electron-molecular vibration (e-mv) coupling is described explicitly by the third term in Eq. (2). The set of G constants gj denotes linear monomer TT-electron - molecular vibration coupling constants. In the following sections, the indicatrix measurements, electronic and molecular spectroscopies, and other techniques are analyzed as methods of characterizing the organic conductors. 

Table 1 Electron-Molecular Vibration Coupling Constants for TCNQ Salts...

A frequently discussed phenomenon of IR vibrational spectroscopy is the electron - molecular vibration coupling of totally symmetric in-plane molecular modes. As a consequence of coupling to the free carriers, these modes become visible in the IR absorption if the light is polarized parallel to the stacking direction. This effect was first observed in TEA(TCNQ)z (triethylammonium (TCNQ)2), as shown in Fig. 4.8-17a, b. 

BEDT-TTF)4M(CN)4, M=Pt, Ni (6,7) In these compounds [6], the "ET" molecules form tetramerized slipped stacks (Fig. lb), already observed in other P-type "ET" salts, which present a tendency to a 2-D electronic structure. These salts exhibit also the two characteristic electronic (CT) absorption bands (Fig. 2) associated with strong vibronic IR modes, which are temperature-dependent [15]. Indeed, we have shown that there is a variation of the electron-molecular vibration (e-mv) coupling effect, associated with a "Peierls-like" phase transition around 200 K for both salts. These results are confirmed by the investigation of the electrical and the magnetic properties of the Ni(CN)4 salt, which indicate a metal-insulator transition in the same temperature range [9]. Nevertheless, low-temperature structural investigations are needed to fully characterize this phase transition. 

The mvestigation of molecular vibrations is a powerful too which can increase our knowledge on structures and on electron molecular vibrations, which are due to charge oscillation between dimerized molecules, coupled with totally symmetric intramolecular modes Raman scattering studies account for totally symmetric vibrations. In addition, Raman spectroscopy can take advantage of resonant effects. In fact, when resonant conditions are fulfilled, selected molecular vibrations are obtained as well as infor> mation on the electronic manifold involved in the resonance process. 

Fortunately several recently developed experimental techniques have greatly enhanced the sensitivity (see Chap.9) and have therefore enlarged the range of possible applications in biology. One example is the resonanoe Raman effect which takes advantage of the enhanced Raman scattering from molecular vibration coupled to an electronic transition, when the excitation wavelength coincides with an electronic transition of the molecule [14.27]. 

There have been numerous applications of continuum models to equilibria and reactions in solution surveys of these and extensive listings are provided by Cramer and Truhlar.16 Other studies have focused upon the effects of solvents upon solute molecular properties, such as electronic and vibrational spectra,16 dipole moments, nuclear quadrupole and spin-spin coupling constants and circular dichroism.12... 

Non-Adiabatic Molecular Hamiltonian. Canonical Transformation Coupling Electronic and Vibrational... 

The coupling of electronic and vibrational motions is studied by two canonical transformations, namely, normal coordinate transformation and momentum transformation on molecular Hamiltonian. It is shown that by these transformations we can pass from crude approximation to adiabatic approximation and then to non-adiahatic (diabatic) Hamiltonian. This leads to renormalized fermions and renotmahzed diabatic phonons. Simple calculations on H2, HD, and D2 systems are performed and compared with previous approaches. Finally, the problem of reducing diabatic Hamiltonian to adiabatic and crude adiabatic is discussed in the broader context of electronic quasi-degeneracy. 

Non-adiabatic molecular Hamiltonian. Canonical transformation coupling 383 electronic and vibrational motions... 

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