Sulfur Raman spectra

Nitric acid has a peak in the Raman spectrum. When nitric acid is dissolved in concentrated sulfuric acid, the peak disappears and two new peaks appear, one at 1400cm attributable to NOj and one at 1050cm due to... 

First attempts to model the vibrational spectrum of polymeric sulfur have been reported by Dultz et al. who assumed a planar zig-zag chain structure [172]. The calculated vibrational DOS was in qualitative agreement with the observed Raman spectrum of fibrous sulfur. However, some details of the spectrum like the relative intensities of the modes as well as the size of the gap between stretching and bending vibrations could not be reproduced exactly by this simplified model [172]. 

Fig. 29 Raman spectrum of p-S at high pressure and room temperature [109]. The wavenumbers indicated are given for the actual pressure. No signals of other allotropes have been detected. The line at 48 cm (ca. 25 cm atp 0 GPa) may arise from lattice vibrations, while the other lines resemble the typical pattern of internal vibrations of sulfur molecules...

Since the vibrational spectra of sulfur allotropes are characteristic for their molecular and crystalline structure, vibrational spectroscopy has become a valuable tool in structural studies besides X-ray diffraction techniques. In particular, Raman spectroscopy on sulfur samples at high pressures is much easier to perform than IR spectroscopical studies due to technical demands (e.g., throughput of the IR beam, spectral range in the far-infrared). On the other hand, application of laser radiation for exciting the Raman spectrum may cause photo-induced structural changes. High-pressure phase transitions and structures of elemental sulfur at high pressures were already discussed in [1]. 

At least five high-pressure allotropes of sulfur have been observed by Raman spectroscopy up to about 40 GPa the spectra of which differ significantly from those of a-Sg at high pressures photo-induced amorphous sulfur (a-S) [57, 58, 109, 119, 184-186], photo-induced sulfur (p-S) [57, 58, 109, 119, 184, 186-191], rhombohedral Se [58, 109, 137, 184, 186, 188, 191], high-pressure low-temperature sulfur (hplt-S) [137, 184, 192], and polymeric sulfur (S ) [58, 109, 119, 193]. The Raman spectra of two of these d-lotropes, a-S and S, were discussed in the preceding section. The Raman spectra of p-S and hplt-S have only been reported for samples at high-pressure conditions. The structure of both allotropes are imknown. The Raman spectrum of Se at STP conditions is discussed below. 

Fig. 31 Evolution of the Raman spectra of a high-pressure and photo-induced sample of Se while decreasing the pressure at ca. 300 K [109]. The spectrum at 3.9 GPa shows the onset of the transformation S6 p-S. The asterisks indicate the Raman signals typical for p-S whereas the peaks of two stretching vibrations of p-S coincide with those of Se at about 458 cm and 471 cm (not indicated by asterisks). The Raman spectrum of the sample recovered at ambient pressure (0 GPa) is evidently a superposition of the spectra of a-Sg and polymeric sulfur, Sj, arrows indicate plasma lines of the Ar ion laser at 515 nm, which have been used for calibration). For Raman spectra under increasing pressure, see Fig. 23 in [1] and references cited therein...

Raman spectroscopy is a useful probe for detecting transannular S - S interactions in bicyclic or cage S-N molecules or ions. The strongly Raman active vibrations occur at frequencies in the range 180-300 cm-1, and for S- -S distances in the range 2.4-2.7 A. On the basis of symmetry considerations, the Raman spectrum of the mixed sulfur-selenium nitride S2Se2N4 was assigned to the 1,5- rather than the 1,3- isomer.37... 

The differences in selection rules between Raman and infrared spectroscopy define the ideal situations for each. Raman spectroscopy performs well on compounds with double or triple bonds, different isomers, sulfur-containing and symmetric species. The Raman spectrum of water is extremely weak so direct measurements of aqueous systems are easy to do. Polar solvents also typically have weak Raman spectra, enabling direct measurement of samples in these solvents. Some rough rules to predict the relative strength of Raman intensity from certain vibrations are [7] ... 

Raman scattering from crystalline S3, SCg, and cyclic selenium sulfides is very intense. The Raman spectrum of 1,2,3-86385 is shown in Fig. 3 as a typical example of the spectra of mixed Se Sg species. The first Raman spectra of liquid and solid sulfur-selenjum phases were reported in 1968 by Ward For a mixture of composition SCqojSo js he observed nine weak Raman lines not present in the spectrum of Sg and assigned them to different Se Sg (n = 0-4) molecules by comparison with the spectra of 8g and 8eg. According to the more recent calculations the assignment given in Table 4 is the most likely one. 

An illustrative example of the influence of symmetry on the number of vibrations is provided by the homologous series of cyclic sulfur allotropes S (n = 6-12). The IR absorptions for these ring systems are weak owing to the low polarity of S-S bonds. However, sulfur is a good Raman scatterer because S-S bonds are readily polarised. The various sulfur allotropes have different symmetries in addition to a different number of sulfur atoms and, consequently, each allotrope exhibits a characteristic Raman spectrum (Figure 3.8). ... 

Trithiocarbonato complexes resemble in their reactions and properties other 1,1-dithiolo complexes such as those of xanthates and dithiocarbamates (see Chapter 16.4). Oxidation of [Ni(CS3)2]2- by iodine or elemental sulfur yields [Ni(CS4)2]2-, which probably has the structure (44). The frequency v(S—S) occurs at 480 cm-1 in the Raman spectrum, while v(C—S) occurs at 1035 cm-1, i.e. at slightly higher energy than in the spectrum of [Ni(CS3)2]2-. The complex (Ph4 As)2-[Ni(CS4)2] can also be prepared from KCS4.148... 

As-prepared EG shows evidence for the presence of carbonyl and hydroxyl groups on the surface, After further treatment of EG with a nitric and sulfuric acid mixture, we obtained a water solution of EG, along with the insoluble portion of the sample which settled out. The infrared (IR) spectrum of the soluble part obtained after drying shows a prominent band due to carbonyl groups in addition to a broad band due to -OH groups as shown in Fig. 8(a). The Raman spectrum of the water-soluble EG shown in Fig. 8(b) exhibits the characteristic G, D and 2D... 

ABj molecules For bent species (Ca,.,), three vibrations should be detected in the IR spectrum as well as in the Raman spectrum. Sulfur dihalides provide a good example to demonstrate this fact SF2 (Ne matrix) shows the following absorptions in the IR spectrum i(SF2) = 834 cm" (FSF) = 358 cm" Vas (SF2) = 808 cm (Haas and Willner, 1978). Since SF2 is un.stable with respect to disproportionation, no Raman spectrum has yet been obtained. However, the IR and the Raman spectrum of SCI2 can easily be measured r j(S- Cl2) = 527 cm r u.dS Ch) = 525 cm" (IR, Ne matrix), (Bielefeld and Willner, 1980) <5(C1SC1) = 208 cm" (Frankiss and Harrison, 1975). In both cases, the expected bent structure is derived from the IR spectrum as well as from the Raman spectrum by simply counting the number of bands. 

The Raman spectrum of Hg3 + (AsF0)2 in sulfur dioxide solution shows in addition to peaks attributable to AsFg and the solvent, a single strong polarized band at 118 cm which was assigned to a Hg-Hg stretch indicating that Hgg has the linear structure Hg" -Hg-Hg +. ... 

Rg. 3. Composition dependence of the isotropic Raman spectrum in the 0-H stretching region for aqueous sulfuric acid solutions. 

Figure 5.8. Raman spectrum of elemental sulfur obtained at 514.5 nm with a Dilor X-Y triple...

Figure 9.12. FT-Raman spectrum of solid sulfur, obtained with a Bruker 66 FTIR and Raman attachment. Filter rejection band blocks Raman shifts from -f-55 to —130 cm. Small feature at zero shift is the residual elastic scatter transmitted by the rejection filter.

FIGURE 11.11 Raman spectrum of thin sp carbon films /z = 50 nm (a), after heating at 150 C in vacuum (b) and h= 150nm (c) and doped with sulfur. 

As other sulfur homocycles, S13 shows a very characteristic Raman spectrum. In the solid state the molecules are of approximate C2 synmietry [38]. 

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