Raman spectra band assignments

In another attempt to obtain diamond from SiC, no evidence for diamond growth was found by means of XRD and SEM after hydrothermal hydrolysis of P SiC powder at 140 MPa and 800°C [57]. Formation of quartz, a second acicular phase, graphite and maybe nanosized diamond crystals was reported. TEM analysis of whiskers of the second acicular phase revealed lattice spacing of 0.9 nm, a <7-value of 0.56nm and a composition of SiOi 6Co.2- A very sharp band at 1330cm was found in a Raman spectrum and assigned to the silicon oxycarbide, SiOi 6C0.2, rather than to diamond. 

The temperature- and pressure-dependences of the Raman bands of ai symmetry of quartz were measured over the ranges 23-800 °C and 0.1-2.1 GPa. " IR and Raman spectra were used to probe the structure of vitreous Si02. In the Raman spectrum, bands near 606 and 495 cm were assigned to vibrations of trimeric and tetrameric rings respectively. " The temperature-dependence of low-wavenumber IR modes of vitreous Si02 was reported. ... 

The structure of the CuNO ionic pair in acetone was investigated by Castro and Jagodzinski [262] using far-infrared and low-frequency Raman spectroscopy and normal coordinate analysis. Three possible structures (C monodentate, C2V monodentate, and C2V bidentate) were studied theoretically. The result obtained for the Civ bidentate structure fits the observed frequencies much better, with an average error of 4 cm , further providing an accurate reproduction of the N isotopic shifts. Two ill-resolved bands observed in the low-frequency Raman spectrum are assigned to the Cu—O2 symmetric (330 cm ) and antisymmetric (347 cm ) stretching. 

The complex studied first was the addition product of antimony trichloride and benzene (119). Two bands at 1236 and 477 cm in the Raman spectrum were assigned to metal-ring vibrations. More recent Raman work 120, 121), as well as infrared studies 122, 123), show definitely that the ring ligand does not retain the original Dg , symmetry of the free hydrocarbon. A C3 or even C2 structure seems to account for the observed spectra most plausibly. 

The infrared and Raman spectra of many alkyl and arylthiazoles have been recorded. Band assignment and more fundamental work has been undertaken on a small number of derivatives. Several papers have been dedicated to the interpretation of infrared spectra (128-134, 860), but they are not always in agreement with each other. However, the work of Chouteau (99, 135) is noteworthy. The infrared spectrum of thiazole consists of 18 normal vibrations as well as harmonic and combination bands. 

The room temperature Raman spectrum excited in pre-resonance conditions [351 indeed shows bands at 169 cm-1 and 306 cm, which are in agreement with the modes observed in the fluorescence spectrum and that have been assigned by ab initio calculations to totally symmetric vibrations jl3). 

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). 

It can be seen from Figures 3.7 and 3.8 that the calculations reproduce very well not only the experimental spectra but also the experimentally observed isotopic shifts indicating a high reliability of the computational method. According to this comparison, definite attribution can be made for even the difficult Raman bands that cannot be assigned based solely on the experimental results. It is, however, necessary to mention at this point that the calculated Raman spectrum provided directly by the ab initio computations correspond to the normal Raman spectrum with the band intensity determined by the polarizability of the correlating vibration. Since the intensity pattern exhibited by the experimentally recorded resonance Raman spectrum is due to the resonance enhancement effect of a particular chromophore, with no consideration of this effect, the calculated intensity pattern may, in many... 

The Raman spectrum of sodium valproate as shown in Figure 7 was obtained in the solid state on a Cary Model 83 Spectrometer. The following bands (cm l) have been assigned for Figure 7 (1). 

The spectra of methane, adsorbed at 90° K., showed a weak band at 2,899 cm.", in addition to a strong band (vt) at 3,006 cm. h This weak band was assigned to the I l symmetrical breathing frequency of methane, which is normally observed only in the bulk state in the Raman spectrum at 2,916 cm. h No over-all dipole change is associated with the vi vibration consequently, it is forbidden in the infrared spectra of liquid and gaseous methane. The appearance of this band is a direct measure of the... 

---