Silica Raman spectrum

Figure 8. Comparison of sucrose Raman spectra obtained using PCF and solid-core silica pump fibers, (a) spectra obtained using about 30 mW excitation at 532 nm (lO-s exposure) each spectrum was normalized to the intensity of the large sucrose peak at 850 cm, (b) difference spectrum (solid-core - PCF) showing residual silica Raman excited by stray 532 nm light within solid-core silica collection fibers the inset shows a (smoothed) silica Raman spectrum obtained using a different instrument with excitation at 257.2 nm.

Fig. 25. Interference of plasma lines from the Ar+ emiasion in the Raman spectrum of a Cab-O-Sil silica sample.

From the Raman spectrum of acetaldehyde adsorbed on silica gel... 

Figure 2. (A) Raman spectrum of silica (B) Raman spectrum of methylated...

Further, in cases where the background fluorescence cannot be entirely eliminated, the Raman spectrum of an adsorbed species appears as a superimposed signal. Figure 2B shows the Raman spectrum of a methylated silica, a sample where all surface Si OH groups have been replaced by SiOCH3 groups. The sharp features near 3000 cm-I due to v(CH) modes will be discussed further later, but the signal to fluorescence intensity can be estimated from the ordinate scale. 

This Raman spectrum shows two new strong features at 112 cm 1 and 400 cm 1, which are not present in the silica background, accompanied by a possible accentuation of the background near 490 cm 1. 

Another good example of using Raman spectroscopy in the polymer industry is to investigate polymer blends. Raman microimages have been used to investigate the spatial distributions of the components in a blend of brominated poly(isobutylene-co-para-methylstyrene (BIMS) and cis-1-4-polybutadiene (BR) containing silica, zinc stearate, thiate, and other additives (21). A Raman spectrum of a blend is shown in Fig. 7-33. Specific bands can be assigned to BIMS, BR, silica, and zinc stearate. A 10 x 10 xm contour... 

Figure 7-33 Typical Raman spectrum for a BIMS-BR blend with silica, zinc stearate, thiate U, and other additives, (a) A band at about 490cm-1 assigned to silica (b) a band at 714cm-1 assigned to the CH2 rocking mode of the BIMS backbone (c) a band at 1,118cm-1 assigned to hydrocarbon chain vibrations of zinc stearate (d) a band at 1,648 cm-1 assigned to the C=C stretching vibrations of the cis-polybutadiene backbone. (Reproduced with permission from Ref. 21.)...

Figure 12.13. Raman spectrum of a typical silica optical fiber, showing eommon Raman features from siliea 514.5 nm exeitation. (Adapted from Referenee 17 with permission.)...

Emissions from both the and the previously unreported lli states of the IF molecule have been observed in the gas-phase reaction of L with F2 at low pressure a four-centre complex has been proposed as the reaction intermediate. A combined theoretical-experimental programme has been conducted to establish techniques for the study of excited-state transitions in Ij and IC1. Experimental techniques based on two-step excitation using two synchronized, tunable lasers have been developed, and successfully applied to excited-state fluorescence measurements on ICl. lodine(i) chloride adsorbed on silica gives the same Raman spectrum as that obtained from adsorbed l2. ... 

The Raman characterization of silica gels is a by-product of researches on the sol-gel process to obtain silica glasses at low temperature from solutions of tetraalkoxysilanes. These spectra have two puzzling features that are also observed in the Raman spectrum of fused, vitreous (v) silica. Two peaks, at 490 cm-1 (called Di) and 604 cm-1 (called D2), are superimposed on the broad band at about 440 cm-1, which is the most intense signal in the spectrum of u-Si02. These two peaks are unusually... 

Surface of a Fumed Silica. Several results obtained for silica A, as received and after some contact with air, can be rationalized in the following way. The low silanol surface density (about 3.65 OH per square nanometer, internal silanols excluded), the comparatively high fraction of geminal sites (/g = 0.21), and the presence of a rather strong D2 band in the Raman spectrum indicate an only partial and selective hydrolysis of the surface after the manufacturing of silica A at high temperature. 

Filled polymers or composites containing silica, clay, or similar materials may have less interference from the filler in the Raman spectrum than in the IR spectrum of the polymer because most fillers are poor Raman scatterers but give strong infrared bands that interfere with polymer identification. It may not be necessary to remove the filler in order to obtain a good Raman spectrum, but such a step is usually necessary for IR. 

The vOH absorbance profile of fully dehydrated silica A, G, P is shown in Figure 26.4. A narrow absorption at 3747 cm dominates the spectrum of silica A and characterizes isolated silanols on surfaces that are not completely hydroxylated. This last statement is also based on the Raman spectrum discussed later. About 9% of the silanols are internal, inaccessible to D2O molecules at room temperature (vOH = 3670 cm Figure 26.4). The weakness of the components at 3715 and 3530 cm is also characteristic of fumed silica samples [3]. 

As provided by the supplier, the Raman spectrum of the sample A is quite different from that usually observed for a silica gel before a thermal pretreatment, because it displays a comparatively strong band D2 at 607 cm (Figure 26.7). Moreover the spectra of samples C and P display a more intense band at 975-980 cm . The intensity of this last band which is assigned at the stretching... 

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