Raman line intensity

A spectroscopic technique that is associated with the enhancement of Raman line intensities upon photon absorption in the electronic spectral range corresponding to an absorption peak. See Raman Spectroscopy... 

Resonance Raman scattering refers to a phenomenon in which Raman line intensities are greatly enhanced by excilalion with wavelengtbs that closely approach that of an electronic absorption band of an analyte. Under this circumstance, the magnitudes of Raman... 

The partitioning of acrylonitrile between particles and the aqueous phase of polybutadiene latex was measured by Raman spectroscopy using rubber latex as substrate. Raman line intensities yielded the partition values in the two phases (295). 

The absolute intensity of the Raman scattered light can be described mathematically, to a good approximation, by using the equations of Placzek s theory (see Box 8.1). Because it is actually possible to calculate the Raman line intensities, and compare them with observations, Raman spectroscopy can be (and... 

The essential assumption of Placzek s theory for Raman line intensities is that the frequency of the exciting radiation vl is larger than the frequency associated with the energy difference between two ro-vibrational states Vvib,rot> but is less than the frequency associated with an electronically excited energy level Vei- In general, this is easy to realize in the majority of Raman scattering experiments. For the Stokes and anti-Stokes line intensities and one finds... 

Raman line intensities are proportional to the number density N of molecules in the initial state /c>, which is in turn proportional to the pertinent Boltzmann factor for that state at thermal equilibrium. Consequently, the relative intensities of a Stokes transition /c> - m> and the corresponding anti-Stokes transition m> -> /c> are 1 and exp — hoj kjkT), respectively. (The factor coicol varies little between the Stokes and anti-Stokes lines, because the Raman frequency shifts are ordinarily small compared to cui.) Hence the anti-Stokes Raman transitions (which require molecules in vibrationally excited initial states) are considerably less intense than their Stokes counterparts, particularly when the Raman shift (o k is large. In much of the current vibrational Raman literature, only the Stokes spectrum is reported (cf Fig. 10.1). 

Raman data collected into spectra contains a lot of information. However, this information is not usually directly available and the data must be processed to get qualitative and quantitative chemical informations. The main fact is that Raman line intensities are proportional to the concentration of chemical components and the Raman line positions are characteristics of the chemical bonding. Nevertheless, some phenomena like undesirable fluorescence, band overlapping, noise and spikes (outlier points) complicate the experimenter s task. 

For homodyne detection, the TR-CRS intensity (for Lorentzian Raman lines) is of the fomi [115]... 

Raman Spectroscopy. Raman spectroscopy is an excellent method for the analysis of deuterium containing mixtures, particularly for any of the diatomic H—D—T molecules. For these, it is possible to predict absolute light scattering intensities for the rotational Raman lines. Hence, absolute analyses are possible, at least in principle. The scattering intensities for the diatomic hydrogen isotope species is comparable to that of dinitrogen, N2, and thus easily observed. 

In the low frequency region, the calculations predict nanotube-specifiic Eig and E g modes around 116 cm and 377 cm respectively, for (10,10) armchair naiiotubes, but their intensities are expected to be lower than that for the A g mode. However, these Eig and E2g modes are important, since they also show a diameter dependence of their mode frequencies. In the very low frequency region below 30 cm a strong low frequency Raman-active E2g mode is expected. However, it is difficult to observe Raman lines in the very low frequency region, where the background Rayleigh scattered is very strong. 

The number and intensity of the Raman lines and the magnitude of the Raman shift can be related to the identity, structure, and bonding of the molecules of the compound scattering the light. 

Since Raman scattered light intensity is very weak, of the order of 10-7 of the excitation line intensity, more powerful laser sources than the He-Ne laser are often needed. The Ar+ laser emits various lines in the region from 457.9 nm to 514.5 nm, of which the most powerful lines (typically — 700 mW) at 488.0 nm (blue) and 514.5 nm (green) are preferred. Furthermore, two other factors which favor the use of the high frequency excitation lines are the peak sensitivity of the photomultipliers in this blue-green region (Fig. 8) and the fourth power Raman intensity law... 

Characteristic Raman Lines and Their Relative Intensities for Various Pyridine (Py)... 

Spectral changes on adsorption are of three types appearance of inactive fundamentals (often coincident with infrared absorptions—see Table IX), shifts in Raman line positions for active vibrations, changes in relative peak intensities, and changes in half-bandwidths. The first three types of change have been reported for centrosymmetric adsorbates. 

The infra-red measurements were of two types, normal-film measurements with the sample sandwiched between KBr plates, and tilted-film experiments with the sample sandwiched between 45° prisms of KBr, in each case with layers of Nujol to provide optical matching. Whereas the 1616 cm 1 Raman line occurs in a region well clear of other lines so that it was satisfactory to measure peak intensities, the infra-red spectrum of PET shows many overlapping bands. Accurate assessment of absorption intensities therefore requires the computer separation of the spectrum into a set of overlapping peaks (shown to be Lorentzian in profile) and a linear background. The procedures adopted and the band assignments are discussed in detail by Hutchinson et al. 6). 

In addition, intensity changes under increasing pressure have been observed. For example, the most intense Raman line at STP conditions is the flg component of v ( 220 cm ), but at about 2 GPa the intensity decreases in favor of the ag component of Vi ( 475 cm ) which on further compression gains more intensity (about a factor of 2 at 5 GPa) [120]. This behavior was explained by the anisotropy of the crystal s compressibihty [139] and differences in the components of the Raman tensor of the two modes [87] with respect to the crystal axes [109]. 

Table 7 Raman and infrared spectra of cycloheptasulfur (wavenumbers in cm Raman intensities in brackets, abbreviations b broad, sh shoulder, v very, s strong, m medium, w weak). Raman lines below 100 cm are lattice vibrations [81]...

Table 11 Raman lines of crystalline S14 at -100 °C. Wavenumbers in cm relative intensities in parentheses (sh shoulder) [165]...

A Raman spectrum of p-S is shown in Fig. 29. While the Raman lines in the stretching region (430-520 cm ) are of high intensity, exceeding those... 

The SO stretching vibration gives rise to a very strong infrared absorption at 1112 cm (in CHBr3), and Raman lines of medium intensity have been observed at 1092 cm for a-SsO and at 1102 cm for PS O. The SS stretch-... 

The probability of Raman scattering is quite small. This normally requires the use of intense laser sources and concentrated samples. A high-resolution double or triple monochromator is used to separate the Raman lines from the intense Raleigh line. 

The vibrational spectrum of a metal complex is one of the most convenient and unambigious methods of characterization. However, it has not been possible to study the interactions of metal ions and biological polymers in this way since the number of vibrational bands from the polymer obscure the metal spectrum. The use of laser techniques for Raman spectroscopy now make it very likely that the Raman spectra of metals in the presence of large amounts of biological material will be measured (34). The intensity of Raman lines from metal-ligand vibrations can be... 

A simple line scan with Raman microscopy, however, clearly showed the LLDPE-MAH layer as a ca. 5-p.m broad plateau from the evaluation of three different Raman band intensities (Figure 14). In this case a simple Raman line scan obviously is the better choice for a determination of the LLDPE-MAH layer thickness, superior even to IR-ATR imaging. We used three Raman bands... 

Figure 14 (a) Raman spectra of the individual layers 1, LLDPE-MAH 2, COPA 3, EVA (abscissa wavenumber (cm ), ordinate intensity in arbitrary units), (b) Raman line scan of polymer laminate using three different Raman bands (abscissa position in pm, ordinate intensity in arbitrary units). 

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