Raman band width

From the Raman band width, it is evaluated that the standard deviation of the stress is 2 GPa, which is five times greater than the mean stress. 

Since then, the vibrational spectrum of Ss has been the subject of several studies (Raman [79, 95-100], infrared [101, 102]). However, because of the large number of vibrations in the crystal it is obvious that a full assignment would only be successful if an oriented single-crystal is studied at different polarizations in order to deconvolute the crystal components with respect to their symmetry. Polarized Raman spectra of samples at about 300 K have been reported by Ozin [103] and by Arthur and Mackenzie [104]. In Figs. 2 and 3 examples of polarized Raman and FTIR spectra of a-Ss at room temperature are shown. If the sample is exposed to low temperatures the band-widths can enormously be reduced (from several wavenumbers down to less than 0.1-1 cm ) permitting further improvements in the assignment. 

In this section, we will describe some experiments which we have performed using the above-mentioned nano-Raman microscope. Figure 2.6a shows the Raman spectmm of an adenine nanocrystal of height 7 nm and width 30 nm [19]. Several Raman bands are observed as the probe tip is near enough to the sample (AFM operation is made in contact mode). These bands, except the one appearing at 924 cm, are assigned as the vibrational modes, inherent to the adenine molecule, according to the molecular orbital calculation. For examples, two major bands, one at... 

Ultrafast time-resolved resonance Raman (TR ) spectroscopy experiments need to consider the relationship of the laser pulse bandwidth to its temporal pulse width since the bandwidth of the laser should not be broader than the bandwidth of the Raman bands of interest. The change in energy versus the change in time Heisenberg uncertainty principle relationship can be applied to ultrafast laser pulses and the relationship between the spectral and temporal widths of ultrafast transform-limited Gaussian laser pulse can be expressed as... 

Among the various methods, the B3-LYP based DFT procedure appears to provide a very cost-effective, satisfactory and accurate means of determining the vibrational frequencies. As an example. Figures 3.7 and 3.8 display direct comparisons between the ground state experimental and DFT B3-LYP/6-31G calculated Raman spectra for DMABN and its ring deuterated isotopmer DMABN-d4. ° The experimental spectra are normal Raman spectra recorded in solid phase with 532nm excitation. For the calculated spectra, a Lorentzian function with a fixed band width of —10 cm was used to produce the vibrational band and the computed frequencies were scaled by a factor of 0.9614. 

In this review, the vibrational spectra of solid chalcogenometallates are presented and a critical discussion of the results given. Initially, measurements of powdered, crystalline samples with isolated ions or molecules are presented followed by single crystal Raman studies which are rarer. Additionally, a group of topics including the interpretation of Raman band intensities and widths. Resonance Raman spectra, the influence of pressure, temperature and sample preparation will be discussed. 

Thus each band in a Raman spectrum represents the interaction of the incident light with a certain atomic vibrations. Atomic vibrations, in turn, are controlled by the sizes, valences and masses of the atomic species of which the sample is composed, the bond forces between these atoms, and the symmetry of their arrangement in the crystal structure. These factors affect not only the frequencies of atomic vibrations and the observed Raman shifts, respectively, but also the number of observed Raman bands, their relative intensities, their widths and their polarization. Therefore, Raman spectra are highly specific for a certain type of sample and can be used for the identification and structural characterization of unknowns. 

A third example can be taken from analytical chemistry. Absorption and resonance Raman spectra of phenol blue were measured in liquid and supercritical solvents to determine the solvent dependence of absorption bandwidth and spectral shifts. Good correlation between absorption peak shift and resonance Raman bands and between Raman bands and bandwidth of C-N stretching mode were observed while anomalous solvent effect on the absorption bandwidth occnrred in liquid solvents. Large band-widths of absorption and resonance Raman spectra were seen in supercritical solvents as compared to liquid solvents. This was dne to the small refractive indices of the supercritical solvents. The large refractive index of the liqnid solvents only make the absorption peak shifts withont broadening the absorption spectra (Yamaguchi et al., 1997). 

IR and Raman studies of the A—H stretching mode (it is important to note that frequency, band width, and intensity are all useful criteria). 

Here, and are total wavefunctions of the m and e states, respectively, and pa is the a component of the electric dipole moment. Te is the band width of the eth state, and the iYe term is called the damping constant. In normal Raman scattering, v0 is chosen so that vo vem Namely, the energy of the incident beam is much smaller than that of an electronic transition. Under these conditions, the Raman intensity is proportional to (vo - vm )4. As vo approaches vem, the denominator of the first term in the brackets of Eq. (1-63)... 

Pressed pellets of BaTiC>3 were sintered in a platinum dish for six hours at 900°C in a controlled partial pressure of oxygen. The samples were quenched to room temperature, and the spectra recorded on a four-slit double-monochromator Raman spectrophotometer. An Ar+ laser with excitation at 514.5 nm was the source. The spectra were recorded at room temperature. Figure 4-30 shows the spectrum of BaTiC>3 whose Ba/Ti ratio is equal to 0.9999. The Raman spectrum is sensitive to the Ba/Ti ratio and theoxygen non-stoichiometry. The half-band width is variable as well as the intensity ratio of the 525 and 713 cm-1 bands. The ratio (I525/713) is at a minimum at the composition of 0.9999, and this can be observed in Fig. 4-31, which shows a plot of the intensity ratio (I525//713) vs. the Ba/Ti composition. 

Figure 4-30 A Raman spectrum of BaTi03 for Ba/Ti = 0.9999 with spectral parameters (intensities and half-band width) defined. This sample was quenched after 3 hours in 1 atm oxygen. (Reproduced with permission from Ref. 51.)...

Sample Coke (IR) H/C (mol/mol, element analysis) Width 1600 cm-1 Raman band (cm-1) ... 

Bulk HfSz is an indirect band gap semiconductor with au indirect band gap energy of 2.1 eV.67 The reflectance spectrum of the nanotubes shows a small blue shift compared with the bulk. The photoluminescence spectrum of the nanotubes shows a band at 676 nm due to trapped states, and the band is blue-shifted with respect to that of bulk HfS2 powder (see Fig. 21a). The Raman spectrum of the HfSz nanotubes is shown in Fig, 21b. It shows a band due to the Aiemode, corresponding to the S atom vibration along the c-axis perpendicular to the basal plane, and another due to the Eg mode due to the movement of the S and Hf atoms in the basal plane.68 The full-width at half maximum (FWHM) of the Alg band is 11 cm 1 in the nanotubes compared to 8 cm 1 for the bulk sample. Such broadening of the Raman band has been noted with MoS2 and WS2 nanotubes.19... 

Fig. 15. Resonance Raman spectra of the Fe +-02 stretching frequency region of bovine heart cytochrome c oxidase 0.1 ms after initiation of the reaction of the fully reduced enzyme with O2. Spectra on the left- and right-hand sides are the observed spectra and the calculated spectra with the differences of the observed versus calculated spectra, respectively. Spectrum (d) is obtained using the following calculation [Spectrum ( )—Spectrum (c)]/2. (e) Simulated bands for Fe— 02 (1), Fe—(2), Fe—(3), and Fe— 02 (4). The peak intensity ratio is 6 6 5 5. All bands have the Gaussian band shape with a half-maximal band width of 12.9cm h...

Raman spectroscopy can be used to detect normal modes of target molecules and also to monitor spectra of Raman labels that are used for one of the spectroscopic bar-codes. Raman bands in the vibrational Raman spectmm have intrinsically narrow bandwidths of ca. 10 cm, which, for example, correspond to less than 0.5 nm width in the visible region below 800 nm. The fluorescence of dye molecules has a broad bandwidth of 100 nm more or less. Hence, spectral overlap between fluorescence bands is inevitable and limits their use for multiplexed analysis. Quantum dots (QDs) have narrower bandwidth than dye-based fluorescence but stUl have broad bands that are several tens of nanometers. Light scattering of noble metal nanoparticles caused by surface plasmon resonance is also... 

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