Calibration Raman intensity

An optical cell for pressures of up to 200 MPa and temperatures to 200°C is presented in Chapter 4.3.4. The cell can be coupled with a commercial Raman spectrometer to measure the course of the intensity of a bond s signal with time. By calibration, the intensity versus time curve can be converted into a concentration versus time curve, from which the rate of reaction and kinetic parameters can be evaluated. The method is explained in Chapter 3.3.2, considering the decomposition of an organic peroxide. 

The necessary derivations with respect to the small displacements can be performed either numerically, or, more recently, also analytically. These analytical methods have developed very rapidly in the past few years, allowing complete ab initio calculation of the spectra (frequencies and intensities) of medium sized molecules, such as furan, pyrrole, and thiophene (Simandiras et al., 1988) however, with this approach the method has reached its present limit. Similar calculations are obviously possible at the semi-empirical level and can be applied to larger systems. Different comparative studies have shown that the precise calculation of infrared and Raman intensities makes it necessary to consider a large number of excited states (Voisin et al., 1992). The complete quantum chemical calculation of a spectrum will therefore remain an exercise which can only be perfomied for relatively small molecule. For larger systems, the classical electro-optical parameters or polar tensors which are calibrated by quantum chemical methods applied to small molecules, will remain an attractive alternative. For intensity calculations the local density method is also increasing their capabilities and yield accurate results with comparatively reduced computer performance (Dobbs and Dixon, 1994). 

The Raman intensities of several rotational and rotovibrational lines of or N2 are accurately known, and it is straightforward to express CILS intensities relative to these known intensities. This can be done by either adding a small amount of the calibration substance (H2) to the gas under investigation ( internal standard ) or by using separate gas cells for the two ( external standard ). 

An ideal luminescent standard for Raman intensity calibration would have several characteristics (17), some of which are difficult to achieve ... 

V. Sivaprakasam and D. K. Killinger, Effect of polarization and geometrical factors on quantitative laser induced fluorescence-to-Raman intensity ratios of water samples and a new calibration technique, J. Opt. Soc. Am. B 20,1980 (2003). 

For a simple unoriented mixture of two tactically pure samples of a vinyl polymer, measurement of the ratio of the IR absorbances or Raman intensities of two modes, one specific for isotactic and one for syndiotactic material, would be a measure of the ratio of the isotactic and syndiotactic contents. Even in this ideal case the method would require calibration with known mixtures of the two types of polymer, because it is not possible to predict how the absolute values of the absorbances or Raman intensities depend on concentration, but only that they are proportional to the concentration. 

Raman spectroscopy was established by means of a comparative study and by calibration to be a suitable non-destructive method for determination of monomer concentration in solid PMMA samples. Although the effect of the internal field on the refractive index and on the Raman intensity of a polymer solution in a monomer was considered, the Raman scattering cross-section of the carbonyl stretching vibration of the monomer was shown to be twice as large as that of the polymer. 42 refs. EUROPEAN COMMUNITY GERMANY WESTERN EUROPE Accession no.483275... 

The absolute Raman intensities of CO have been measured by Cahill and Leroi (1969a) by observing the lattice modes and an intramolecular mode during the same experiment. This procedure produced relative measurements which were calibrated by using absolute gas phase measurements for the COj internal mode available in the literature. It was found that the observed intensities agreed very well with those predicted by a theory similar to that described in Section IV.C. 

Neat PE was also studied in the melt. The 2930 cm"l and 2850 cm"l bands behave as expected from the alkane study. A plot of the ratio of their intensities versus temperature is shown in Fig. 6. The function is also a straight line and parallel to the lines for neat n-C and diluted n-C2 5 in COCl3(Fig. 5). Therefore, the same procedure can be used to calibrate the mentioned Raman intensities for PE as was used for li this way, a quantitative measurement of the gauche bond content of a linear polymer can be obtained. 

Data Calibration. The CCD detector provides count as a function of pixel position. The data required by the user are Raman intensity as a function of Raman shift. The... 

ES Etz, WS Hurst, SJ Choquette. Raman intensity calibration with glass luminescence standards. In DB Williams, R Shimizu, eds. Institute of Physics Conference Series No. 165. Philadelphia Institute of Physics, 2000, pp 121-122. 

As a side aspect, the HPLC-Raman correlation results allow us to calibrate the RRS instruments in terms of carotenoid concentration. According to the regression analysis, the cumulative skin carotenoid content c, measured in pg per g of skin tissue, is linked to the height of the C=C RRS skin carotenoid intensity, I, via c [pg/g]=4.3 x 10 5=/ [photon counts]. Integrating the RRS spectra with the instrument s data acquiring software therefore allows us to display skin carotenoid content directly in concentration units, i.e., in pg carotenoid content per g of tissue. 

The Raman technique allows us to determine the intensity of Raman bands, and thereby to quantify the concentration of the chemical components in a complicated mixture (a Beer s law calibration graph of intensity against concentration is advisable see Section 9.1). 

Table 1 gives a comparison of Raman and pmr results for a series of copolymers. In the pmr data of Figure the CHg absorption of the polymer backbone at 6O.8 to 3.0 partially overlaps with the CH doublet centered at S2.h and this reduces the accuracy of the integrated intensity of the ester moiety to no better than 25. On the other hand, the accuracy of the Raman data is on the order of 3%, so the two techniques do agree within experimental error. The error associated with the Raman method could be reduced if calibration curves were employed. The weight percent feed and polymer compositions were converted to mole percent and reactivity ratios for MMA and OM were calculated by the Yezrielev, Erokhina and Riskin (YBR) method (9). The following equation, derived from the copolymer... 

Owing to the very high rate of decomposition, in-situ measurement of concentration by means of Raman spectroscopy was applied. The peroxide used was f-butylperoxy pivalate (see Chapter 5.1, Table 5.1-2) dissolved in n-heptane at a concentration of 1 wt.%. In order to observe the change in intensity of absorption of the 0-0 bond at 861 cm 1, the spectrometer was adjusted to this wave number. The change of intensity is an indication of the reduction in the peroxide concentration, and was recorded as a function of time. The apparatus was calibrated before measuring the intensity of peroxide solutions of different concentrations [22],... 

Fig. 2.9. A Average Raman spectra of hyperplastic (n = 20 solid line) and adenomatous (n = 34 broken line) colon polyps collected ex vivo (power = 200 mW 30-s collection time). B Average Raman spectra of hyperplastic (n = 9 solid line) and adenomatous (n = 10 broken line) colon polyps collected in vivo (power = 100mW 5-s collection time). The spectra have been intensity corrected, wavelength calibrated, and fluorescence background subtracted (modified from [25], with permission)...

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