O. Sala

Surface enhanced Raman spectra of benzotriazole adsorbed on a copper electrode

Abstract The surface-enhanced Raman spectra of benzotriazole adsorbed on a silver electrode have been investigated in order to study the formation of complexes at the electrode surface as a function of the applied potential, the pH and the type of halide in the electrolyte solution. The use of a pseudo-halide, SCN−, in the electrolyte (KNO3) solution allowed the simultaneous adsorption of SCN− and benzotriazole to be followed.

TiO2 with a high sulfate content—thermogravimetric analysis, determination of acid sites by infrared spectroscopy and catalytic activity

Sulfated metal oxides have a very high acidity, being considered by some as superacids, although it is still a controversial matter. There has been considerable investigation into sulfated ZrO2 in recent years, but sulfated TiO2 has been relatively neglected. There is evidence that the Bronsted acid sites would be responsible for the high levels of acidity and catalytic activity in sulfated ZrO2, since these sites would be present in samples with higher sulfate content. In order to verify whether for sulfated TiO2, a high level of acidity also occurs in samples with a higher sulfate content, samples were prepared with elevated levels of sulfate. Characterization was carried out through thermogravimetric analysis, determination of acid sites by infrared spectroscopy, through adsorption of pyridine and measurement of the catalytic activity in the isomerization reaction of n-hexane. It was verified that samples with elevated sulfate content were actually those which had Bronsted acid sites and a higher catalytic activity in the isomerization reation of n-hexane. It was also verified that the sulfate loss in the thermogravimetric analysis occurred at different temperatures, depending on the sulfate content of the sample.

Vibrational spectrum and force constants of the monochlorochromate ion

Abstract The vibrational spectrum of the ion (CrO3Cl)− is reported. The Raman spectra were obtained in the red region of the spectrum by excitation with the helium radiations 5875.6 and 6678.2 A, the infra-red absorption spectrum was investigated over the range 10–32 μ. The spectrum is in full agreement with the expected C3v -symmetry of the ion and the observed frequencies have been assigned under this point group. A normal co-ordinate treatment based upon Wilsons -FG-matrix method and a simplified valence force field has been carried out and force constants have been calculated. The stretching frequencies of the ion and the related valence force constants are compared with those of other hexavalent chromium compounds, previously reported by the authors.

Vibrational analysis of nicotinic acid species based on ab initio molecular orbital calculations

Abstract In this work a vibrational investigation of the equilibrium species in aqueous solution of nicotinic acid was performed, by both experimental as well as theoretical methods. The Raman spectra of its aqueous solutions at some pH values were obtained and analyzed considering the equilibrium of three main species: a totally protonated one, a zwitterionic form, and the nicotinate anion. These species were also studied by ab initio (Hartree–Fock and second-order Moller–Plesset perturbation) and hybrid density functional theory calculations. The structures of these species were optimized and the vibrational frequencies calculated. These methods provided a good correlation between the calculated and the experimental vibrational frequencies. A great mixing of the ring vibrational modes, as well as between the ring and the substituent modes, was observed.

Raman spectra of pyridine adsorbed on a copper electrode

Abstract The surface enhanced Raman scattering (SERS) of pyridine adsorbed on a copper electrode was observed with 647.1 nm excitation and the dependence of the Raman intensity as a function of electrode potential was obtained for the most intense bands. The results are compared with reported intensity and frequency values for the silver/pyridine system.

Vibrational spectrum and normal co-ordinate analysis of the monofluorochromate ion

Abstract The vibrational spectrum of the ion [CrO 3 F] − is reported. Raman spectra of KCrO 3 F dissolved in diluted hydrofluoric acid were obtained in the red region of the spectrum by excitation with helium radiations 5875.6 and 6678.2 A. The infrared absorption spectrum of the solid compound in Nujol mull was investigated over the range 10–60 μ; further absorption measurements were made on solutions of KCrO 3 F in acetone. The observed vibrational spectrum is consistent with that expected for the isolated ion [CrO 3 F] − of symmetry C 3 v . Making use of the observed frequencies assigned to the normal modes and of wilsons FG -matrix method the force constants of the ion have been calculated under the assumption of a “diagonal” valence force field. The L -matrix and the potential energy distribution among the internal symmetry co-ordinates are reported and compared with the corresponding values obtained for the ion [CrO 3 Cl] − .

Cyclic-fluorovoltammetry as a technical tool in the study of passivating films generated on electrode surfaces☆

Abstract The methodology developed to study the behaviour of the fluorescence intensity of passivating films generated electrochemically on a copper electrode simultaneously with the current and charge vs. voltage curves is presented. This kind of study has been called cyclic-fluorovoltammetry. The cyclic-fluorovoltammograms of a copper electrode in aqueous halide solutions containing benzotriazole (BTAH) at different pHs have been investigated in order to study the formation of cuprous complexes as passivating species. The effect of the addition of benzylamine to the working solution has also been investigated. The presence of some complexes involving Cu(I), BTAH or benzotriazolate (BTA − ) and the halide has been characterized.

SERS effect of isonicotinic acid adsorbed on a copper electrode

Abstract The surface enhanced Raman spectra (SERS) of isonicotinic acid adsorbed on a copper electrode were obtained in order to verify their dependence on the type of electrolyte solution, pH and applied potential. The results are discussed considering the most characteristic bands of the species (protonated or nonprotonated) in the ring nitrogen and in the carboxylic group. In specifically adsorbed electrolytes (Cl − and mainly I − ) the completely protonated species is more stabilized on the electrode surface than it is in non-specifically adsorbed anions (ClO − 4 ), because of the formation of ion pairs with the coadsorbed halide ions. For more negative potentials, even at low pH values, the spectra are characteristic of the nonprotonated species.

Evidences for a localized chromophore in the Ti(IV)/squarate complex: a resonance Raman investigation.

The present work continues a previous investigation on the interaction of oxocarbonic anions with highly charged metal ions. When squarate or croconate solutions are added to Ti(IV) acidic solutions, a rather strong and broad band shows up that is not present in the optical spectrum of the reagents. Excitation of the Raman spectrum of the resulting coloured solutions close to their absorption maxima leads to the enhancement of several modes of the oxocarbon. In particular the totally symmetric nu(C=O) mode of the Ti(IV)/squarate or croconate complexes shows an outstanding enhancement, a completely different behaviour of that observed in the Raman spectrum of the free oxocarbons, where the nu(CO) modes are barely observed. Such result indicates a rather strong Ti(IV)-oxocarbon interaction via the CO moieties with the formation of a strongly allowed LMCT (ligand to metal charge transfer) state. In addition the rather selective enhancement of the nu(CO) modes strongly suggests that the chromophore involved in the LMCT state is highly localized in the Ti(IV)-CO moieties of the complexes and that the enhancement mechanism involved is very likely the one described by Albrechts A term, i.e. Franck-Condon one state mechanism.

Overtone spectrum of the CH chromophore in CHI3

The infrared spectrum of iodoform vapor was measured between 900 and 10 000 cm−1 in a heatable multipass cell with an interferometric Fourier transform spectrometer and temperatures up to 433 K. Twenty‐five bands (including hot bands) could be assigned as fundamentals, overtone, or combination bands of the CH stretching and bending vibrations. The observed data are interpreted in terms of variational calculations using internal and normal coordinates and some evidence is given for the existence of a strong coupling constant ‖ksbb′‖=50 cm−1 between the two vibrational modes with subpicosecond redistribution of energy. Off‐diagonal anharmonic constants between the CH stretching and bending manifold and the molecular frame vibrations have been determined.