Raman Correction

The special features of the optics and the frequency dependent scattering, which occur in a Raman spectrum, can be reduced to a high degree by using this correction. There is an undo function for this correction. The file selection is limited to Raman spectra. 

The theoretical background for the Scatter Correction is that the scattering intensity is a function of the wavenumber (Rayleigh s v -law, see Section 5.7). The effect increases with the spectral distance of the line of interest from the wavenumber of the excitation laser. To correct this the Raman intensity data are multiplied point-by-point by  

By checking the Reference Correction box the effects of the spectrometer optics can be corrected for. This requires a spectrum of a tungsten lamp for calibration. 

High Folding Limit Low Foldhg Limit Number of Sample Scans Scan time (sec) 

Running Sample Number Peak Amplitude Peak Location Sample Spacing Divisor Instrument Type Focal Length 

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Erequency Calibration T Raman Correction Black Body... 

Figure 10.36. List of instrument parameters with Raman correction flags added.

Potassium hydrogen monoperoxosulfate monohydrate [14696-73-2] KHSO 20, related to the triple salt, is not made commercially. The crystal stmcture has been determined and some features of its Raman and ir spectra recorded (69). This compound is more stable under x-rays than the triple salt. The 0—0 distance is 0.1460 nm. The dihedral angle of the 0—0 moiety is about 90°, similar to that ia soHd hydrogea peroxide. This compouad is reported as toxic and irritating to eyes, skin, and mucous membranes (2). Although undoubtedly correct, this description probably better relates to the triple salt. 

IR and Raman studies of heterocycles today cover two different fields. For simple and symmetrical molecules very elaborate experiments (argon matrices, isotopic labelling) and complex calculations lead to the complete assignment of the fundamentals, tones and harmonics. However, the description of modes ought to be only approximate, since in a molecule like pyrazole there are no pure ones. This means that it is not correct to write that the band at 878 cm is y(CH), and the only correct assertion is that the y(CH) mode contributes to the band. On the other hand, IR spectroscopy is used as an analytical tool for identifying structures, and in this case, bands are assigned to r-iCO) or 5(NH) on the basis of a simple Nujol mull spectrum and conventional tables. Both atttitudes, almost antagonistic to each other, are discussed in this section. 

In the Bom-Oppenheimer picture the nuclei move on a potential energy surface (PES) which is a solution to the electronic Schrodinger equation. The PES is independent of the nuclear masses (i.e. it is the same for isotopic molecules), this is not the case when working in the adiabatic approximation since the diagonal correction (and mass polarization) depends on the nuclear masses. Solution of (3.16) for the nuclear wave function leads to energy levels for molecular vibrations (Section 13.1) and rotations, which in turn are the fundamentals for many forms of spectroscopy, such as IR, Raman, microwave etc. 

Raman spectra of S2 in its triplet ground state have been recorded both in sulfur vapor and after matrix isolation using various noble gases. The stretching mode was observed at 715 cm in the gas phase [46], and at 716 cm in an argon matrix [71]. From UV absorption and fluorescence spectra of sulfur vapor the harmonic fundamental mode of the S2 ground state was derived as t e = 726 cm . The value corrected for anharmonicity is 720 cm [26, 27]. Earlier reports on the infrared absorption spectrum of 2 in matrix isolated sulfur vapor [72] are in error the observed bands at 660, 668 and 680 cm are due to S4 [17] and other species [73]. 

Figure 5.4 Resonance Raman spectrum of [Au2(dcpm)2](CI04)2 in acetonitrile solution at room temperature taken with 282.4 nm excitation, after intensity corrections and subtractions of the Rayleigh line, glass bands, and solvent bands. Reproduced with permission from [7a]. Copyright (1999) American Chemical Society.

The macular region of the retina is optically relatively easily accessible. The excitation and the Raman light must traverse the cornea, lens, and vitreous, sketched in Figure 6.3a, all of which are generally of sufficient clarity for optical measurements. Correction factors can be expected to be required... 

The advantage of Raman spectromicroscopy is that very small specimens can be studied while still allowing the determination of the second and fourth moments of the ODF. However, the expressions for the Raman intensities are more complex since the optical effects induced by the microscope objective have to be considered. Although the corrections may be small, they are not necessarily negligible [59]. This problem was first treated by Turrell [59-61] and later by Sourisseau and coworkers [5]. Turrell has mathematically quantified the depolarization of the incident electric field in the focal plane of the objective and the collection efficiency of the scattered light by high numerical aperture objectives. For brevity, only the main results of the calculations will be presented. Readers interested in more details are referred to book chapters and reviews of Turrell or Sourisseau [5,59,61]. The intensity in Raman spectromicroscopy is given by [59-61]... 

If the "localized" formulation of the structure of Ru(bpy)3 as Ru(III)(bpy)2(bpy ) + is realistic, the resonance Raman spectrum of Ru(bpy)3+ can be predicted. A set of seven prominent symmetric modes should be observed at approximately the frequencies seen in Ru(III)(bpy)3, with approximately two thirds of the intensity of the ground state bpy modes. The intensity of the isolated 1609 cm - peak fits this prediction, as do the other "unshifted" peaks. A second set of seven prominent Raman modes at frequencies approximating those of bpy should also be observed. Figure 6 shows that this prediction is correct. The seven Ru(bpy)3+ peaks which show substantial (average 60 cm l) shifts from the ground state frequencies may be correlated one-for-one with peaks of Li+(bpy ) with an average deviation of 10 cm. In addition, the weak 1370 cm l mode in Ru(bpy)3 is correlated with a bpy mode at 1351 cnfl. It is somewhat uncertain whether the 1486 cm l bpy mode should be correlated with the Ru(bpy)3 mode at 1500 cm -1- or 1482 cm 1. It appears clear that the proper formulation of Ru(bpy)3 is Ru(III)(bpy)2(bpy ). This conclusion requires reinterpretation of a large volume of photophysical data (43,45,51 and references therein). 

Attention should be paid to possible problems in the measurement of fluorescence quantum yields (some of which are discussed Section 6.1.5) inner filter effects, possible wavelength effects on Op, refractive index corrections, polarization effects, temperature effects, impurity effects, photochemical instability and Raman scattering. 

In general, electrostatic theory is not able to reproduce correct energy surfaces as a whole since the compensation of errors mentioned above holds only around the energy minima (see p. 25). Furthermore, the various spectral data, especially IR, RAMAN and NMR results, which became accessible during the last ten years cannot be interpreted at all by electrostatic models. Many theoreticians feel, therefore, that there is a need for more accurate calculations on ion-molecule complexes based upon quantum mechanics. 

Note added in proof. It is not certain that the H20(as) studied by Hardin and Harvey and Buontempo is the low density form. Given the sensitivity of the form of deposit to conditions such as deposition rate and surface temperature, it is conceivable that it was the high density form. Indeed, V. Mazzacurati and M. Nardone, Chem. Phys. Lett. 32, 99 (1975) studied the Raman spectrum of H20(as) deposited at 110 K. Although their sample was heavily contaminated with crystalline ice, an estimated spectral contour for H20(as) can be obtained. This contour, which if correct is almost certainly that of the low density form, is very different from that reported by Li and Devlin and by Venkatesh, Rice and Bates (see following text). 

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