Raman electron scattering

Almost every modem spectroscopic approach can be used to study matter at high pressures. Early experiments include NMR [ ], ESR [ ] vibrational infrared [33] and Raman [ ] electronic absorption, reflection and emission [23, 24 and 25, 70] x-ray absorption [Tf] and scattering [72], Mossbauer [73] and gems analysis of products recovered from high-pressure photochemical reactions [74]. The literature contains too many studies to do justice to these fields by describing particular examples in detail, and only some general mles, appropriate to many situations, are given. 

Each spectroscopic technique (electronic, vibra-tional/rotational, resonance, etc.) has strengths and weaknesses, which determine its utility for studying polymer additives, either as pure materials or in polymers. The applicability depends on a variety of factors the identity of the particular additive(s) (known/unknown) the amount of sample available the analysis time desired the identity of the polymer matrix and the need for quantitation. The most relevant spectroscopic methods commonly used for studying polymers (excluding surfaces) are IR, Raman (vibrational), NMR, ESR (spin resonance), UV/VIS, fluorescence (electronic) and x-ray or electron scattering. 

K. M. Gough and H. K. Srivastava, J. Phys. Chem., 100, 5210 (1995). Electronic Charge Flow and Raman Trace Scattering Intensities for CH-Stretching Vibrations in n-Pentane. 

As stated in Section 1.4, resonance Raman (RR) scattering occurs when the sample is irradiated with an exciting line whose energy corresponds to that of the electronic transition of a particular chromophoric group in a molecule. Under these conditions, the intensities of Raman bands originating in this chromophore are selectively enhanced by a factor of 103 to 105. This selectivity is important not only for identifying vibrations of this particular chromophore in a complex spectrum, but also for locating its electronic transitions in an absorption spectrum. 

Most experiments do not depend on order parameters of higher rank, e.g. the influence of orientational order on an absorption band is completely described in terms of S and D (Luckhurst, 1993). On the other hand, Raman-spectra being based on a two-photon effect are influenced additionally by the order parameters of the next level, such as the Legendre polynomial P4 (Pershan, 1979). This is of considerable theoretical interest, however, up to now of less importance for practical applications. There are some further experimental techniques for gathering information on the orientational order, among these are fluorescence, neutron and electron scattering. Probably the most reliable method is NMR (Emsley, 1985), however this usually means deuteration of all hydrogen atoms but one. 

Single-electronic-state (SES) limit The Raman spectroscopy in SES limit is where the incident photon energy is very close to, or falls within, the absorption band of an excited electronic state of a molecule, and the resulting Resonance Raman (RR) scattering is dominated by the properties of this resonant electronic state. 

The fundamental role of the dynamic electron-phonon coupling in the Jahn-Teller crystals was clearly demonstrated by the Raman light scattering experiments [18],... 

Table 1. Experimental data that indicates H - H quantum entanglement in condensed matter. Neutron experiments are described in the text. Raman and electron scattering experiments are published in Refs. [Chatzidimitriou-Dreismann 1995 Chatzidimitriou-Dreismann 2003 (a)] respectively. Raman scattering has also a time window in the fs-range.

Fig. 18.1 A dressed-state model that is used in the text to describe absorption, emission, and elastic (Rayleigh) and inelastic (Raman) light scattering. g) and. v> represent particular vibronic levels associated with the lower (1) and upper (2) electronic states, respectively. These are levels associated with the nuclear potential surfaces of electronic states 1 and 2 (schematically represented hy the parabolas). Rj are radiative continua— 1 -photon-dressed vibronic levels of the lower electronic states. The quasi-continuum L represents a nonradiative channel—the high-energy regime of the vibronic manifold of electronic state 1. Note that the molecular dipole operator /t couples ground (g) and excited (s) molecular states, but the ensuing process occurs between quasi-degenerate dressed states g,k and 5,0).

Fig. 3. Electronic Raman scattering from the /-multiplet levels of Smj Yj.Se at 80 K for sl.O for = 0.05, the La-substituted Sm jjLao ojSe is shown. The scattering configuration is the same as in fig. 2. The hatched area indicates the electronic scattering from the J-0-> 1 excitation. Phonon scattering is seen below 200 cm ...

Fig. 4. Polarized Raman spectra of Sm, Y S (x = 0, 0.10, 0.25) and of SmogjGdojjS in the black and pressure-transformed (p>4kbar) gold phase at 80 K. The scattering configuration is the same as in fig. 2. Dashed line below 300 cm , phonon scattering hatched area, electronic scattering form the / = 0— 1 excitation.

To obtain reliable experimental data and to correctly interpret them, we used such physicochemical and analytical techniques as dilatometry, viscometiy, UV and IR spectroscopy, electroiuc paramagnetic resonance, Raman light scattering spectroscopy, electron microscopy, and gas-liquid chromatography. To analyze the properties of polymeric dispersions, the turbidity spectrum method was used, and the efficiency of flocculants was estimated gravimetrically and by the sedimentation speed of special water-suspended imitators (e.g. copper oxide). 

Resonance Raman and antisymmetric scattering are involved in a novel technique involving spin-flip Raman transitions in paramagnetic molecules that can function as Raman electron paramagnetic resonance. Figure 3.2a shows a conventional vibrational Stokes resonance Raman process, while 3.2b and 3.2c show the polarization characteristics of the two distinct spin-flip Raman processes for scattering at 90°... 

A great deal of effort has been placed in determining the solvation structure of ions, i.e, the solvent structure in their vicinity, from a variety of spectroscopic techniques such as NMR, XAFS [258-260], Mossbauer, IR, and Raman [261] scattering techniques such as X-rays, electron and neutron diffraction [261,262] electrochemical techniques [2,36] and simulation methods [261]. The rationale behind these studies hinges upon the idea that a realistic description of the thermophysical properties of electrolyte solutions must take into account the ion-induced local distortion of the solvent properties, i.., it should go beyond the so-called continuum or primitive models. The challenge resides in our ability to probe the properties of the solvent in the vicinity of ions, and then, to make explicit contact with meaningful solvation-related macroscopic properties. 

As this review is primarily concerned with low-energy electronic scattering in the normal and superconducting states of high-rc superconductors, it is useful to consider in detail the cross-section for Raman scattering from intraband electronic excitations. Using eqs. (6) and (7), the electronic Raman scattering cross-section can be related to a correlation function associated with an effective density p. 

Note that the isotropic part (Z, = 0) of the Raman scattering vertex in eqs. (15) and (16), which comprises the entire electronic scattering response in the absence of interband... 

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