Raman spectra for

Raman spectra are naturally closely related to the photodissociation cross sections for vibrationally excited parent molecules. The latter contain, without any doubt, more details about the potential energy surfaces in the lower as well as the upper states, but on the other hand, they are more difficult to measure. Compared to the experiments described in Chapter 13, which requires three lasers, Raman spectra are rather cheap to obtain. 

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Fig. IV-14. Resonance Raman Spectra for cetyl orange using 457.9-nm excitation. [From T. Takenaka and H. Fukuzaki, Resonance Raman Spectra of Insoluble Monolayers Spread on a Water Surface, J. Raman Spectr., 8, 151 (1979) (Ref. 157). Copyright Heyden and Son, Ltd., 1979 reprinted by permission of John Wiley and Sons, Ltd.]...

The behavior of insoluble monolayers at the hydrocarbon-water interface has been studied to some extent. In general, a values for straight-chain acids and alcohols are greater at a given film pressure than if spread at the water-air interface. This is perhaps to be expected since the nonpolar phase should tend to reduce the cohesion between the hydrocarbon tails. See Ref. 91 for early reviews. Takenaka [92] has reported polarized resonance Raman spectra for an azo dye monolayer at the CCl4-water interface some conclusions as to orientation were possible. A mean-held theory based on Lennard-Jones potentials has been used to model an amphiphile at an oil-water interface one conclusion was that the depth of the interfacial region can be relatively large [93]. 

Fig. 25. Room temperature Raman spectra for purified single-wall carbon nanotubes excited at five different laser wavelengths, showing evidence for the resonant enhancement effect. As a consequence of the ID density of states, specific nanotubes (n, m) are resonant at each laser frequency [195].

We ve included several papers in the References section which perform theoretical and experimental studies of the IR and Raman spectra for these compounds. These compounds were among the earliest ab initio frequency studies of such systems. In addition, in the case of propellane, theoretical predictions of its energy and structure preceded its synthesis. 

Fig. 7. Low-temperature (77 K) resonance Raman spectra for A. vinelandii Fdl, T. thermophilus Fd, D. gigas Fdll, and ferricyanide-treated C. pasteurianuni Fd obtained with 488.0-nm excitation. Taken with permission from Ref. (17).

A group of investigators recently suggested that the density-functional theory (DFT), which calculates IR and Raman spectra, is a useful tool for direct characterization of the structures of diamondoids with increasing complexity [66]. They applied DFT to calculate Raman spectra whose frequencies and relative intensities were shown to be in excellent agreement with the experimental Raman spectra for C26H30, thus providing direct vibrational proof of its existence. 

Figure 5, In situ Raman spectra for Fe-TsPc adsorbed on Ag(lOO), Ag(lll) and Ag(llO) at 0.2 V vs. SCE in 0.1 M HCIO4 Ar saturated aqueous solutions (15).

Figure 2.9 Spectra of a single adenine nanocrystal, (a) TERS spectrum, (b) ordinal SERS spectrum, and (c) ordinary near-infrared (NIR) Raman spectra. For the SERS measurement, a silver island film was used. For the NIR Raman measurement, i thick sample of adenine was used with a 1 h exposure.

FIG. 65. Raman spectra for films deposited employing the chemical annealing technique for different hydrogen exposure times. 10. 20. and 30.5 seconds. 

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. 

Raman spectra (for both the solid state and aqueous solution) provide better fingerprints for heparins than their i.r. spectra.79 However, the application of Raman spectroscopy to glycosaminoglycans is less routine than with i.r., both for instrumental reasons and because of possible interference from traces of fluorescent impurities.77... 

The same bands were resolved in the resonance Raman spectra for the PSII membranes (Ruban et al., unpublished). Therefore, this method, for example, can be used to assess whether the LHCII trimers are intact in vivo at various physiological conditions. 

Figure 8.16 (a) IR and (b) Raman spectra for the mineral calcite, CaC03. The estimated density of vibrational states is given in (c) while the deconvolution of the total heat capacity into contributions from the acoustic and internal optic modes as well as from the optic continuum is given in (d). 

Figure 1.13 Raman spectra for a number of transition metal oxides supported on y-AI203 [75,102], Three distinct regions can be differentiated in these spectra, namely, the peaks around 1000 cm-1 assigned to the stretching frequency of terminal metal-oxygen double bonds, the features about 900 cm 1 corresponding to metal-oxygen stretches in tetrahedral coordination sites, and the low-frequency (<400 cm-1) range associated with oxygen-metal-oxygen deformation modes. Raman spectroscopy can clearly complement IR data for the characterization of solid catalysts. (Reproduced with permission from The American Chemical Society.)...

More evidence for the existence of several conformational isomers, at least in liquid and gaseous substances comes from infrared and also Raman spectra. For example each conformer has its own I.R. spectrum, but the peak positions are often different. Thus the C-F bond in equatorial fluorocyclohexane absorbs at 1062 Cm-1, the axial C-F bonds absorbes at 1129 Cm . So the study of infrared spectrum tells, which conformation a molecule has. Not only this, it also helps to tell what percentage of each conformation is present in a mixture and since there is relationship between configuration and conformation in cyclic compounds the configuration can also be frequently determined. 

Ultrafast spectroscopy is so important because it provides dynamical information that is very hard or impossible to access from IR and Raman spectra. For systems with a single chromophore, this dynamical information is often characterized by the frequency TCF,... 

Figure 3c. Comparison of observed resonance Raman spectra for isotope mixture with predicted spectra for two possible coordination geometries.

L-Alanine, the simplest chiral amino acid, has been the subject of the most extensive study and serves as the prototype for the other amino acids. A complete vibrational assigrunent has been obtained (85, 86) based on solution phase IR and Raman spectra and solid phase Raman spectra for alanine-do, alanine-C -di, alanine-C(3-d3, and alanine-C -d-C -d3. In the CH stretching region, the antisymmetric methyl stretches are assigned at 3006 and 2989 cm , the methine stretch at 2970 cm , and the Fermi resonance diad involving the symmetric methyl stretch and the overtone of the antisymmetric methyl deformation at 2950 and 2893 cm. The calculated frequency for the unperturbed symmetric methyl stretch is 2930 cm . 

Another area of laser use applied to expl materials involves its employment to excite Raman spectra for studies of crystal structure, lattice dynamics, phase transitions and vibrational mode frequencies. Compds studied include T1N3 (Refs 10, 17 23), NaN3 (Ref 18), KN3 and RbN3 (Ref 4), NH4N3 (Ref 7), BaN3 (Refs 5, 8 24), LA (Ref 9), HMX (Ref 25), RDX (Ref 11) and Amm perchlorate (Ref 26)... 

We have shown [46] that the same situation as for [C4Cilm]+ exisfs for longer alkyl chain systems, at least for the l-hexyl-3-methylimidazolium cation. Raman spectra for [CgCjIm]+ cation systems have bands at 698, 623, and 601 cm (but no distinct band at -498 cm i). A comparison between typical experimental spectra is shown in Figure 12.15. 

Figure 12.24 Experimental FT-Raman spectra for the [CjC4pyr][Tf2N] liquid (in the figure [bmpy][Tf2N]) (Fujimori, T., Fujii, K., Kanzaki, R., Chiba, K., Yamamoto, H., Umebayashi, Y., and ishiguro, S.-i., /. Mol. Liquids 131-132, 216-224, 2007), showing that the spectum (top) at room temperature essentially consists of bands from both the [Tf2N] anion (middle) and the [CiC4pyr]+ cation (bottom) (shifted conveniently). The Fi+ and Cl do not contribute bands directly in the liquid but have influence on the structures of the salts and are interactive with the ions and influence the conformational equilibria in the IF (Berg, R. W., Unpublished results, 2006.)...

Figure 2. Low-frequency Raman spectra for solid (Et4NXHCr2(CO) o) (upper) and (Ef42V)2-(Cr2(CO)io) (lower)...

The rule of mutual exclusion states that for a molecule with a center of symmetry, a given vibrational transition cannot appear in both the IR and Raman spectra. (For the proof, see Chapter 9.) Some fundamentals may be both IR and Raman inactive their frequencies can often be determined from IR or Raman combination bands. 

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