Polycrystalline Raman spectra

Most fundamental work on the vibrational spectra of azoles appeared in the period 1960-1980. Examples of more recent work include (i) a complete assignment of the gas-phase IR spectrum of indazole (93JCS(F1)4005) (ii) IR spectral data were used to determine the enthalpies of 0—H. . . N and N—H. . . O bonds in complexes of formic acid and 3,5-dimethylpyrazole (87MI301-01) (iii) the vibrational assignment of the Raman spectrum of polycrystalline pyrazole (92MI301-01) based on 3-21G calculations. 

Figure A.l. Typical Raman spectrum of polycrystalline diamond [325].

Figure 9.7 Typical Raman spectrum of polycrystalline graphite. (Reproduced with permission from G. Turrell and J. Corset, Raman Microscopy, Developments and Applications, Academic Press, Harcourt Brace Company, London. 1996 Elsevier B.V.)...

A film of Ag nanoparticles embedded in a polycrystalline Ce,o matrix was grown by codeposition under high vacuum. The Raman spectrum shift to lower frequency observed... 

Unfortunately, the experimental information for anthracene is not as rich as for naphthalene. Transitions to the lowest 7r-excited state occur at 1.1 eV and are dipole forbidden. In addition, PES [161,162] predicts transitions at 1.76,2.73, and 2.81 eV. The EA spectrum [166] of anthracene recorded in argon matrices agrees with the absorption maxima in organic glasses [140], and the vibronic fine structure is in accord with the Raman spectrum of polycrystalline anthracene [167] at room temperature. The CASSCF/CASPT2 calculations presented by... 

Raman microspectroscopy studies indicate that the spectra from hardness impressions in SiC and those from the pristine surface outside the indentation area are significantly different [4, 134], This is illustrated in Figure 48 for a polycrystalline chemical-vapor deposited (CVD) 3C SiC film. The results for a single crystal 2H poly type of SiC are essentially the same [134], except for the extra line at 770 cm" in the Raman spectrum of pristine 2H SiC, related to the splitting of the TO(T) modes in hexagonal 2H as compared to the cubic 3C SiC [226]. This indicates that the deformation mechanism during indentation of SiC is independent of its microstructure prior to loading. Comparison of a typical spectrum... 

Microwave spectra of (52) and three isotopic species (1- C, 2- C, and 5- C) have been obtained and analysed. Stark effect measurements yield a dipole moment H = 0.299 0.008 D. The i.r. spectra of gaseous, liquid, and polycrystalline bicyclo-[2,2,2]octa-2,5,7-triene, and the Raman spectrum of the liquid, have been obtained. The observed frequencies are reproduced with an average error of +2.0 cm by a 37-parameter potential function. 

The experimental Raman spectrum from polycrystalline dodecyltrimethylammonium is presented at the bottom of Fig. 3b, while the simulated spectrum is depicted at the top. In the latter one four features can be seen. The first one appears as a shoulder at 2866 1/cm, and has already been assigned to the CH2 symmetric stretching mode. The... 

Fig. 3 Comparision between lorentzian-envelop generated Raman spectra, using a fixed line-width of 8 1/cm from heptylpyridinium and the Raman spectrum from a polycrystalline sample of dodecylpyridinium-bromide. A shows the C-C stretching spectral range and B corresponds to the C-H stretching range. The excitation source was the 488 nm line from an Ar ion laser, the scanning rate was 2 l/cm/2s...

Additional evidence that SERS spectra are representative of behavior at majority sites on polycrystalline Ag is the equivalence (shapes and relative band intensities) of the SERS spectrum of pyridine with the surface-unenhanced Raman spectrum of pyridine on smooth Ag. The latter spectrum was observed at high laser power using OMA techniques. The main difference between the two spectra is the narrower bandwidths of the unenhanced spectrum. This result and the results of the above-reported spectroelectrochemical experiments indicate that SERS can be used to elucidate complex redox equilibrium behavior which would be representative of the entire surface. Of course, there are cases where a redox product may not be SERS active. Finally, it should be mentioned also that the Raman processes involved in SERS are extremely fast so that time-resolved SERS should be capable of following the fastest electrochemical dynamic processes of interest. 

Fig. 7.7 Comparison of Raman spectra for carbon nanotubes (1) and normalized G-bands of a single crystalline (2) polycrystalline anisotropic graphite sample with oriented grains and LaiSOO A (3) and the difference spectrum corresponding to the curves 2 and 3 (4). All spectra correspond to room temperature and excitation with > l=514.5 nm and are normalized to the maximum of the intensity of the corresponding Raman band. The difference spectrum (4) is multiplied by a factor of 3 for better comparison with the other spectra...

Fig. 7.10 Results of numerical deconvolution of the main bands and harmonic tones in Raman spectra into composing lines Vq band of SWCNT (a), V[, band of an isotropic polycrystalline graphite (b), 2vd tone spectrum of SWCNT (c), and Ivj, tone spectrum of the graphite single...

Fig. 5. Shock front rise time in a 700 nm thick sample of polycrystalline anthracene, (a)-(e) Coherent Raman (CARS) spectra of the V4 transition, which blueshifts and broadens when shocked at 4 GPa. The cartoons at right illustrate the progress of the shock front through an impedance-matched sandwich. When the shock front is midway through the anthracene layer, two separate peaks are seen in the CARS spectrum, representing ambient and shocked anthracene. The shock front risetime is considerably shorter than the shock transit time of 180 ps through the 700 nm layer. Detailed analysis shows that tr < 25 ps. Adapted from ref. [35].

The main qualitative predictions of this model are strikingly demonstrated by the low-temperature RRS spectra of crystalline (TTF)Br whose structure consists of almost isolated (TTF+)2 dimers. The electronic absorption spectrum of polycrystalline (TTF)Br at 12 K is shown in Fig. 4a. The long wavelength absorption, displaying a doublet structure around 700 nm,is due to the CT transition of the dimers. The vertical bars indicate the laser wavelengths used to excite the Raman spectra. Those obtained with excitation wavelength at Ao = 530.9 nm and at A = 647.1 nm, resonant with LE and CT transition respectively, are shown in Fig. 4b. 

A single narrow peak due to vSiD was seen in the IR spectrum of D Si(l 11)-(1 X 1). For the analogue containing H rather than D, both vSiH and 5SiH were observed vSiH bands were assigned from the IR spectrum of hydrogenated microcrystalline silicon The Raman spectra of polycrystalline sihcon films prepared by hot-wire CVD show vSiH at 2000 cm only. The IR spectra show an additional band at about 2100 cm for specimens produced at a wire temperature of 1900°C. ... 

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