Raman spectra surface acidity

The vibrational spectrum of 4-pyridine-carboxylic acid on alumina in Fig. 4d is equivalent to an infrared or Raman spectrum and can provide a great deal of information about the structure and bonding characteristics of the molecular layer on the oxide surface. For example, the absence of the characteristic > q mode at 1680 cm 1 and the presence of the symmetric and anti-symmetric O-C-O stretching frequencies at 1380 and 1550 cm indicate that 4-pyridine-carboxylic acid loses a proton and bonds to the aluminum oxide as a carboxylate ion. 

As-prepared EG shows evidence for the presence of carbonyl and hydroxyl groups on the surface, After further treatment of EG with a nitric and sulfuric acid mixture, we obtained a water solution of EG, along with the insoluble portion of the sample which settled out. The infrared (IR) spectrum of the soluble part obtained after drying shows a prominent band due to carbonyl groups in addition to a broad band due to -OH groups as shown in Fig. 8(a). The Raman spectrum of the water-soluble EG shown in Fig. 8(b) exhibits the characteristic G, D and 2D... 

Figure 8.47. Raman spectrum of native form ai- add g tx)pcoteiiL (Bottom) Raman difference spectrum of native tti- acid glycoprotein minus ai acid glycoprotein wMi tiound progesterone. Positions of amino acids with aromatic side chains, wiA respect to their environment or surface of the protein, have been also determined. Cuitosey from Vbdimir Kopecky Jr., ROd er Enrich, Katefina Hofbauoova and Vladimir Baumnic...

The solvent-induced stereochemical behaviour of a bile acid-based biphenyl phosphite has been studied experimentally using circular dichroism (CD) spectroscopy, and theoretically using DFT quantum mechanical methods. " The FTIR, Raman and surface-enhanced Raman scattering (SERS) spectra of phenyl phosphate disodium salt have been recorded and its vibrational wavenumbers, calculated using the Hartree-Fock/6-31G basis set, compared with experimental values. From SERS spectra study, the molecule is adsorbed on the silver surface with the benzene ring in a tilted orientation. The presence of the phenyl ring and the phosphate group vibrations in the SERS spectrum reveal the interactions between the phenyl... 

Figure 8.6 Schematic of adsorption mode of benzotriazole on an iron electrode in sulfuric acid at potentials, (a) Positive to potential of zero charge (PZC) (b) PZC (c) Negative to PZC (d) Normal Raman spectrum of the Fe(ll) BTA complex and potential-dependent surface Raman spectra of BTAH on an iron electrode in saline water.

Figure 14 Improvement in the Raman spectrum of peat humic acid in neutralized form by use of near-infrared excitation. The top spectrum was obtained with 514.5-nm excitation, which results in a large fluorescence background that obscures the signal. However, as shown in the bottom spectrum, with 1064-nm excitation, and after subtraction of thermal emission background, spectral features of peat humic are clearly discernible. (Reprinted with permission from YH Yang, HA Chase. Applications of Raman and surface enhanced Raman scattering techniques to humic substances. Spectr Lett 31 821-848, 1998. Copyright 1998 Marcel Dekker, Inc.)...

This review will endeavor to outline some of the advantages of Raman Spectroscopy and so stimulate interest among workers in the field of surface chemistry to utilize Raman Spectroscopy in the study of surface phenomena. Up to the present time, most of the work has been directed to adsorption on oxide surfaces such as silicas and aluminas. An examination of the spectrum of a molecule adsorbed on such a surface may reveal information as to whether the molecule is physically or chemically adsorbed and whether the adsorption site is a Lewis acid site (an electron deficient site which can accept electrons from the adsorbate molecule) or a Bronsted acid site (a site which can donate a proton to an adsorbate molecule). A specific example of a surface having both Lewis and Bronsted acid sites is provided by silica-aluminas which are used as cracking catalysts. 

Surface-enhanced Raman scattering using a silver-coated alumina support selectively enhanced the spectrum of p-aminobenzoic acid. This allowed the determination of this compound at low ppm levels in vitamin B complex354,355. 

Quite recently the complex of 2-(4-hydroxyphenylazo) benzoic acid (HABA) and avidin was presented as a model system of chromophore-containing proteins [79]. HABA was chosen because its spectrum is known to be very sensitive to the molecule environment, which makes it an ideal probe for eventual structural changes accompanying adsorption of the complex on the Ag electrode surface [79]. The fact that normal solution resonance Raman (RR) and the SERRS spectra of avidin-HABA complex are almost identical and those of free (uncomplexed) HABA are different clearly demonstrates that the native form of the complex is preserved on the surface. HABA-SERS active groups of its complex with avidin are buried within the protein matrix. Hence, it is evident that the long-range electromagnetic effect operates, so that it should be possible to obtain SERS spectra of chromophores buried in more or less native proteins [79]. 

Raman spectra of the two-step acid-base-catalyzed gel (r = 3.8) after drying at 50°C or heating to 200, 600, or 1100°C compared to the spectrum of conventional u-SiOj. Xerbgel samples treated at 50 to 600°C possess high surface areas (>800 m /g), whereas the 1100°C sample and v-SiOi are fully dense (341. 

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