Raman vibrational frequencies

I CRS interferogram with a frequency of A = coj + 2c0j - cOq, where cOp is the detected frequency, coj is the narrowband frequency and coj the Raman (vibrational) frequency. Since cOq and coj are known, Wj may be extracted from the experimentally measured RDOs. Furthemiore, the dephasing rate constant, yj, is detemiined from the observed decay rate constant, y, of the I CRS interferogram. Typically for the I CRS signal coq A 0. That is, the RDOs represent strongly down-converted (even to zero... 

Table 12 Selected IR and Raman Vibrational Frequencies (cm for M(acac)4, M(acac)3X and M(acac)2X2 (X = Cl,...

Raman Vibrational Frequencies ofKeggin Anions (Aqueous Solutions), cm (62. 65. 67. 71)... 

Reduced v(CH) IR or Raman vibrational frequency as a consequence of lowered vibrational force constant. 

Raman vibrational frequencies and intensities for both complexes 5 and 7 are compared in Table II. The relative Raman scattering intensities were calculated from the differential cross sections. For their evaluation we used the wavelength of 613.33 nm (105). Polarizabilities were calculated in the limit of a static perturbation. 

Raman Vibrational Frequencies of Known Chlorogallate Species... 

Figure 9 Sulfur isotope dependence of resonance Raman vibrational frequencies for (a) the [Cu(1.5)-Cu(1.5)] mixed-valence Cua site, obtained with 488-nm excitation (b) the [2Cu(l)2Cu(ll)] Cuz site in semireduced N2O reductase, obtained with 568-mn excitation and (c) the dithionite-reduced Cuz site, obtained with 647-mn excitation. S denotes 230-cm" ice mode from frozen solvent. C denotes a band believed to arise from an altered Cua site. (Reprinted with permission from M.L. Alvarez, J. Ai, W.G. Zumft, J. Sanders-Loehr, and D.M. Dooley, J. Am. Chem. Soc., 2001, 123, 476. 2001 American Chemical Society)...

TABLE 1 Raman vibrational frequencies and caicniated distortions for trniu-W(N2)2(dppe)2... 

Experimental infrared and Raman vibrational frequencies for COFj have been reported by many workers, and the most important data sets are included in Tables 13.18 and 13.19, resepctively. Other studies have been reported [169,1507,2209] and, in addition, the infrared spectrum of gaseous COFj has been included in a catalogue of common molecules [1462a]. 

It has been shown, from simple quantum chemical calculations (MNDO), that F is linearly related to molecular electronic properties, such as Eg, ionisation potential Ip and bandwidth. Fig. 8 [33]. It then becomes possible, in principle, to correlate directly Raman vibrational frequencies with the above electronic properties. The theoretical linear relation has also been verified experimentally, for the case of measured from the UV-visible spectrum, and Fjj derived from Raman experiments. Fig. 9 [3. ... 

Raman vibrational frequencies and intensities of octane, dodecane and hexadecane corrformers were calculated using quantum mechanical ab initio methods. The results agreed with various trends observed in the experimental spectra of alkanes, as well as several observations from the experimental Raman spectra of PEs. The data obtained indicated that ab initio calculated Raman data on alkanes provided valuable information regarding the interpretation of polymer Raman spectra, in particular information concerning issues where interpretation based on experimental verification was not possible. 23 refs. 

Raman vibrational frequencies as a function of Ge concentration in GeSe glasses. Reprinted with permission from FengX.,Bresser W. J., and Boolchand R, Direct evidence for stiffness threshold in chalcogenide glasses, Phys. Rev. Lett, 78,4422-4425 [1997). Copyright (1997) by the American Physical Society. 

Raman vibrational frequencies as a function of MCN in GeAsSe glasses. Reprinted with permission from Wang, R. R, Smith, A., Prasad, A., et al., Raman spectra of Ge,jASj,Sei, j j, glasses,/. Appl. Phys. 106(4], 043520-5 (2009). Copyright (2009), AIR Publishing LLC. 

Raman effect When light of frequency Vo is scattered by molecules of a substance, which have a vibrational frequency of j, the scattered light when analysed spectroscopically has lines of frequency v, where... 

The first temi results in Rayleigh scattering which is at the same frequency as the exciting radiation. The second temi describes Raman scattering. There will be scattered light at (Vq - and (Vq -i- v ), that is at sum and difference frequencies of the excitation field and the vibrational frequency. Since a. x is about a factor of 10 smaller than a, it is necessary to have a very efficient method for dispersing the scattered light. 

Due to the rather stringent requirements placed on the monochromator, a double or triple monocln-omator is typically employed. Because the vibrational frequencies are only several hundred to several thousand cm and the linewidths are only tens of cm it is necessary to use a monochromator with reasonably high resolution. In addition to linewidth issues, it is necessary to suppress the very intense Rayleigh scattering. If a high resolution spectrum is not needed, however, then it is possible to use narrow-band interference filters to block the excitation line, and a low resolution monocln-omator to collect the spectrum. In fact, this is the approach taken with Fourier transfonn Raman spectrometers. 

Time-resolved spectroscopy has become an important field from x-rays to the far-IR. Both IR and Raman spectroscopies have been adapted to time-resolved studies. There have been a large number of studies using time-resolved Raman [39], time-resolved resonance Raman [7] and higher order two-dimensional Raman spectroscopy (which can provide coupling infonuation analogous to two-dimensional NMR studies) [40]. Time-resolved IR has probed neutrals and ions in solution [41, 42], gas phase kmetics [42] and vibrational dynamics of molecules chemisorbed and physisorbed to surfaces [44]- Since vibrational frequencies are very sensitive to the chemical enviromnent, pump-probe studies with IR probe pulses allow stmctiiral changes to... 

Figure Bl.3.7. A WMEL diagram for the seventh order Raman echo. The first two field actions create the usual Raman vibrational coherence which dephases and, to the extent that inliomogeneity is present, also weakens as the coherence from different cliromophores walks oflP. Then such dephasing is stopped when a second pair of field actions converts this coherence into a population of the excited vibrational state / This is followed by yet another pair of field actions which reconvert the population into a vibrational coherence, but now one with phase opposite to the first. Now, with time, the walked-oflP component of the original coherence can reassemble into a polarization peak that produces the Raman echo at frequency oi = 2(o - (O2...

The vibrational states of a molecule are observed experimentally via infrared and Raman spectroscopy. These techniques can help to determine molecular structure and environment. In order to gain such useful information, it is necessary to determine what vibrational motion corresponds to each peak in the spectrum. This assignment can be quite difficult due to the large number of closely spaced peaks possible even in fairly simple molecules. In order to aid in this assignment, many workers use computer simulations to calculate the vibrational frequencies of molecules. This chapter presents a brief description of the various computational techniques available. 

Other Inorganics. Inorganic species in solution have been studied very effectively by Raman spectroscopy. Work in this area includes the investigation of coordination compounds (qv) of fluorine (qv) (40), the characterization of low dimensional materials (41) and coordinated ligands (42), and single-crystal studies (43). Several compilations of characteristic vibrational frequencies of main-group elements have been pubflshed to aid in the identification of these species (44,45). 

Infrared (ir) transmission depends on the vibrational characteristics of the atoms rather than the electrons (see Infrared and Raman spectroscopy). For a diatomic harmonic oscillator, the vibrational frequency is described by... 

Of course, whether the symmetry groups for armchair and zigzag tubules are taken to be (or or T>2 /, the calculated vibrational frequencies will be the same the symmetry assignments for these modes, however, will be different. It is, thus, expected that modes that are Raman or IR-active under or T) i, but are optically silent under S>2 h will only show a weak activity resulting from the fact that the existence of caps lowers the symmetry that would exist for a nanotube of infinite length. 

Atomic charges and electrostatic potentials Vibrational frequencies IR and Raman spectra NMR properties... 

Vibrational frequencies Calculated vibrational frequencies are larger than measured values, typically by about 12%. Systematic scaling of calculated frequencies (by 0.88) leads to values which are generally suitable for assignment and interpretation of experimental infrared/Raman spectra. 

Many of the compounds in higher oxidation states are reactive, and for moisture-sensitive solids that cannot be crystallized, some of the bond lengths quoted in Table 2.1 are from EXAFS measurements [24], Raman spectroscopy is likewise well suited to studying such reactive compounds, and vibrational data for halometallates are given in Table 2.2 trends illustrated include the decrease in frequency as the oxidation state of the metal decreases, and similarly a decrease in vibrational frequency, for a given oxidation state, with increasing mass of the halogen. 

Much earlier information on the structure of diazonium ions than that derived from X-ray analyses (but still useful today) was obtained by infrared spectroscopy. The pioneers in the application of this technique to diazonium and diazo compounds were Le Fevre and his school, who provided the first IR evidence for the triple bonds by identifying the characteristic stretching vibration band at 2260 cm-1 (Aroney et al., 1955 see also Whetsel et al., 1956). Its frequency lies between the Raman frequency of dinitrogen (2330 cm-1, Schrotter, 1970) and the stretching vibration frequency of the C = N group in benzonitrile (2255 cm-1, Aroney et al., 1955). In substituted benzenediazonium salts the frequency of the NN stretching vibration follows Hammett op relationships. Electron donor substituents reduce the frequency, whereas acceptor substituents increase it. The 4-dimethylamino group, for example, shifts it by 103 cm-1 to 2177 cm-1 (Nuttall et al., 1961). This result supports the hypothesis that... 

There are 78 vibrational degrees of freedom for TgHg and it has been shown that the molecule has 33 different fundamental modes under Oh symmetry, 6 are IR active, 13 are Raman active, and 14 vibrations are inactive. The experimental fundamental IR active vibrational frequencies have been assigned as follows 2277 (v Si-H), 1141 (vas Si-O-Si), 881 5 O-Si-H), 566 ( s O-Si-O), 465 (v O-Si-O), and 399 cm ( s O-Si-O). These generally agree well with calculated values The IR spectrum recorded in the solid state shows bands at 2300 and 2293 cm ... 

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