Raman scattering band shape

The combination of surface enhanced Raman scattering (SERS) and infrared reflection absorption spectroscopy (IRRAS) provides an effective in-situ approach for studying the electrode-electrolyte interface. The extreme sensitivity to surface species of SERS is well known. By using polarization modulation of the infrared beam for IRRAS, the complete band shape is obtained without modulating the electrode potential. 

The shape of the vibration-rotation bands in infrared absorption and Raman scattering experiments on diatomic molecules dissolved in a host fluid have been used to determine2,15 the autocorrelation functions unit vector pointing along the molecular axis and P2(x) is the Legendre polynomial of index 2. These correlation functions measure the rate of rotational reorientation of the molecule in the host fluid. The observed temperature- and density-dependence of these functions yields a great deal of information about reorientation in solids, liquids, and gases. These correlation functions have been successfully evaluated on the basis of molecular models.15... 

Although the localization and shape of the CT bands depend on a degree of charge transfer from the electron donor-to-acceptor molecule, this spectral region is not suitable for evaluation of the amount of transferred electrons in organic conductors. Raman scattering and vibrational spectra are more useful for this purpose. 

In the Raman spectra of Si, the line shape of the optical phonon peak is quite sensitive to degenerate p-type doping as a result of interference of Raman scattering from a continuum of electronic intravalence band transitions (electronic Raman scattering) with that from discrete phonon excitations (vibrational or phonon... 

In Ih phase, the selection rules for D6h are violated due to the proton disorder. So the observed band shape represents mostly the phonon density of states (DOS). As shown in Fig.2 (b), observed Raman spectra in the librational region in Ih phase surprisingly agrees with results of the neutron scattering (IINS) and MD calculation. In XI phase, Raman spectra show mostly the first order scattering around the T -point but qualitative agreement with neutron and MD studies is also seen in XI phases. 

In practice, one usually defines a training set of molecules and associated experimental properties and fits the relevant data with an assumed force field.The next step is to test the results on molecules and data outside the training set. Experimental data that depend on the energy surface and that may be used to determine the parameters of the intramolecular interactions consist mainly of gas-phase structural data derived from microwave spectra or electron diffraction patterns, crystal structures derived from X-ray and inelastic neutron scattering measurements, and vibrational frequencies obtained from infrared and Raman spectra. Torsional barriers are derived from NMR band shapes and relaxation times, whereas conformational energies are determined from spectroscopic and thermochemical data. Nonbonded parameters are determined mainly from... 

What are the consequences of these considerations for depolarized light scattering In a dilute gas where reorientation is predominantly inertial, we expect the spectrum to be what is normally called the pure rotational Raman spectrum of the molecule. As higher densities are approached, the discrete spectral lines broaden and overlap to form a continuous band. We show how the band shape can be computed for freely rotating linear molecules and spherical top molecules and then indicate the assumptions that have been used by several authors to include collisions in the theory. 

The phenomenon of surface-enhanced infrared absorption (SEIRA) spectroscopy involves the intensity enhancement of vibrational bands of adsorbates that usually bond through contain carboxylic acid or thiol groups onto thin nanoparticulate metallic films that have been deposited on an appropriate substrate. SEIRA spectra obey the surface selection rule in the same way as reflection-absorption spectra of thin films on smooth metal substrates. When the metal nanoparticles become in close contact, i.e., start to exceed the percolation limit, the bands in the adsorbate spectra start to assume a dispersive shape. Unlike surface-enhanced Raman scattering, which is usually only observed with silver, gold and, albeit less frequently, copper, SEIRA is observed with most metals, including platinum and even zinc. The mechanism of SEIRA is still being discussed but the enhancement and shape of the bands is best modeled by the Bruggeman representation of effective medium theory with plasmonic mechanism pla dng a relatively minor role. At the end of this report, three applications of SEIRA, namely spectroelectrochemical measurements, the fabrication of sensors, and biochemical applications, are discussed. 

The three main quantities, which can be derived from an experiment in infrared absorption spectroscopy, or Raman scattering, are (i) vibrational frequencies, (ii) integrated intensities and (iii) band shapes [1]. Each of these quantities can provide independent information on the local and/or overall dynamics and electrical properties of molecules. In this paper we shall not discuss case (iii), since it has not yet been applied extensively to the case of conducting polymers. 

Before discussing vibration-rotation band shapes, it is appropriate to consider "pure rotational" Raman spectra in dense fluids (often called inelastic light scattering). The argument closely parallels that for i.r. absorption, but with the added complication of polarized and depolarized scattering. In the depolarized case, one has a "self" term which is ... 

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