The effect of nitrate on the reduction of TCE by commercial granular iron was investigated in column experiments designed to allow for the in situ monitoring of the iron surface film with Raman spectroscopy. Three column experiments were conducted; one with an influent solution of 100 mg/l nitrate+1.5 mg/l TCE, and two control columns, one saturated directly with 100 mg/l nitrate solution, the other pre-treated with Millipore water prior to the introduction of a 100 mg/l nitrate solution. In the presence of nitrate, TCE adsorbed onto the iron, but there was little TCE reduction to end-products ethene and ethane. The iron used (Connelly, GPM, Chicago) is a product typical of those used in permeable granular iron walls. The material is covered by an air-formed high-temperature oxidation film, consisting of an inner layer of Fe(3)O(4), and an outer, passive layer of Fe(2)O(3). In the control column pre-treated with Millipore water, the passive Fe(2)O(3) layer was removed upon contact with the water in a manner consistent with an autoreduction reaction. In the TCE+nitrate column and the direct nitrate saturation column, nitrate interfered with the removal of the passive layer and maintained conditions such that high valency protective corrosion species, including Fe(2)O(3) and FeOOH, were stable at the iron surface. The lack of TCE reduction is explained by the presence of these species, as they inhibit both mechanisms proposed for TCE reduction by iron, including catalytic hydrogenation, and direct electron transfer.

Lithium bis(trifluoromethylsulfone)imide (LiTFSI), a promising electrolyte for high energy lithium batteries, forms several stable solvates having low melting points in aprotic solvents. In a previous study (D. Brouillette, G. Perron and J. E. Desnoyers, J. Solution Chem., 1998, 27, 151), it was suggested, based on thermodynamic studies, that such stable solvates may persist in solution and influence their properties. To verify this hypothesis, phase diagrams and Raman spectra have been measured for solutions of LiTFSI in acetonitrile, propylene carbonate and glymes (n(ethyleneglycol) dimethyl ether or Gn), which have the chemical structure CH3-O(CH2-CH2-O)(n)-CH3 for n = 1 to 4 and 10. The relative intensities of the LiTFSI and solvent Raman bands are proportional to the concentration for systems without solvates. The systems for which stable solvates were identified in the phase diagram show important changes in the relative intensities for both the LiTFSI and the solvent Raman bands at concentrations corresponding to particular stoichiometries and support the conclusion that stable solvates are present in the solutions. The structure of the crystalline G1:LiTFSI solvate was determined by X-ray crystallography. Structures for (G2)(2):LiTFSI and (G1)(3):LiTFSI solvates are proposed.

Oxidation of pure mercury electrodes was followed by in situ surface-unenhanced Raman spectroscopy. A special spectroelectrochemical cell allowed the observation of spectral features of the oxidation products using a Raman microprobe. The electrochemical behaviour of mercury in basic solution, halide (F-, Cl-, Br- and I-) and pseudohalide (SCN-) media was investigated. Insoluble films were formed during the anodic processes in all these systems. The identities of the electrochemically generated films were clearly determined from the Raman spectra. The main product of the electrochemical oxidation of mercury in basic solutions was solid HgO. The anodic behaviour of mercury in the presence of halide yielded insoluble Hg2X2 compounds (where X is the halide). The time dependence of the Raman signals indicated a diffusion-controlled growth of the halide films. The oxidation of mercury in SCN- solutions also produced a solid precipitate [Hg-2(SCN)(2)]. Raman bands due to soluble mercury(II) thiocyanate complexes [Hg(SCN)(x)(2-x)], present in the electrochemical diffusion layer, were also observed. Copyright 2002 John Wiley Sons, Ltd.

Commercial poly(dimethylsiloxane) (PDMS) 7-microm solid-phase microextraction (SPME) fibers were used for sampling and Raman spectroscopic analysis of a tailpipe diesel exhaust, candle smoke, cigarette smoke, and asbestos dust. Samples were collected via direct exposure of the SPME fiber to contaminated air. The mass loading for SPME fibers was varied by changing the sampling time. Results indicate that PDMS-coated fibers provide a simple, fast, reusable, and cost-effective air sampling tool for airborne particulates. The PDMS coating was stable; Raman bands of the PDMS coating were observed exactly at the same wavenumber positions before and after air sampling. Raman spectroscopic analysis resulted in identification of several characteristic bands allowing chemical speciation of particulates. The advantage of the SPME fiber is the open bed geometry allowing for application of various spectroscopic methods of particulate analysis. This paper describes the first-ever combined application of SPME technology with Raman confocal microspectroscopy for sampling and analysis of airborne particulates. Advantages of the combination of solid-phase microextraction and Raman microspectroscopy for airborne particulate analysis are discussed. Challenges associated with combined SPME sampling and Raman analysis of single particles are also described.

The nature of the corrosion products generated by localized attack on 1024 mild steel have been investigated in the presence of chloride and/or sulfate ions in bicarbonate and phosphate aqueous solutions. A spectroelectrochemical cell was used for in situ measurements of the Raman spectra of the corrosion products generated during pitting. These products were identified as the so-called green rust compounds. The assignment of the hydroxyl groups in green rust is confirmed by isotopic substitution. The composition of the green rust generated in bicarbonate or phosphate solution containing chloride and/or sulfate ions has been determined. A correlation between the green rust composition and the electrochemical behaviour after the initiation of pitting has been noted and discussed.

Raman spectroscopy has been used to characterize neat alkanethiol and various metal-alkanethiolate materials. Neat alkanethiol gives rise to two CS stretching peaks at 662 and 735 cm−1, assigned to gauche and trans rotamers respectively. Only one CS stretching peak positioned at 725 cm−1 was found from CuC12 and AgC12 layered compounds, implying the absence of gauche rotamer near the thiolate group. An all-trans conformation of the chain is inferred from the peak position values of the CC stretching modes of CuC12 and AgC12 layered compounds. Gauche rotamers were observed in silver colloids capped with alkanethiolate.

The dependence of the surface-enhanced Raman scattering (SERS) of pyrazine (pz), adsorbed on polycrystalline gold electrodes ("smooth" and rough), on both the surface coverage and morphology was investigated. The morphology of the rough gold electrode was observed by atomic force microscopy (AFM), and the surface coverage data were obtained from previous electrochemical measurements. The plots between the SERS intensity of the pz ring-breathing mode (ca. 1016 cm-1) and the surface morphology parameters (roughness factor) were obtained. The SERS intensity reached a maximum between 20 and 30 ORCs. Independent AFM measurements indicated that roughness features with an average size of ca. 100 nm are present in the surface which yielded the strongest SERS signal. The dependence of the SERS intensity on the surface morphology agrees well with the electromagnetic calculations of the enhancement factor for gold spheres. The SERS intensities from pz adsorbed on an "unroughened" gold electrode track the surface concentration up to ca. two-thirds of a monolayer. As the amount of pz in the surface approaches the monolayer value, this dependence becomes inverse, due to the interactions between the induced molecular dipoles present on a heavily packed surface. The SERS intensities from a smooth surface (zero ORC) were obtained by extrapolation from the spectrum of pz adsorbed on gold electrodes with different degrees of roughness. The calculated SERS intensities were compared to the surface coverage, and a linear relationship was obtained for a wide range of potentials.

Electrochemical processes in the mercury-solution interphase were probed by in situ spectroelectrochemical micro-Raman spectroscopy. This is the first report of the in situ characterization of electrochemical processes for a pure mercury electrode by Raman spectroscopy. Mercury was oxidized in 0.1 M KClO4 solution, in the presence and absence of pyridine. Raman spectra, at several applied potentials, of the soluble oxidation products present in the mercury/solution interphase were recorded. The aquated Hg-2(2+) [mercury(I)] cation was the only product observed for mercury oxidation in the absence of pyridine. This cation was characterized by the Hg-Hg stretch band at ca. 175 cm(-1). An Hg-2(2+)-ClO4- precipitate was formed on the electrode surface at very anodic potentials. The oxidation of mercury in the presence of pyridine resulted in the formation of soluble mercury(II)-pyridine complexes in the interphase. Characteristic Raman bands of these complexes were observed at ca. 1023 and 1048 cm(-1). Solution Raman experiments demonstrated that a mixture of mercury(ll)-pyridine complexes [of general formula Hg(py)(n)(2+), where 1 < n < 4] was produced in the interphase. (C) 1998 John Whey & Sons, Ltd.

The surface-enhanced Raman scattering (SERS) spectra of monoprotonated pyrazine cations adsorbed on silver electrodes have been measured. The molecular orientation of the pyrazinium cation is dependent on the electrode potential. At potentials more positive than −170 mV the monoprotonated pyrazine is adsorbed end-on. However, the spectral features suggest a flat orientation as the potential becomes more negative than −300 mV. Monoprotonated pyrazine cations with both orientations can coexist at potentials between these limits. The adsorption of the positive ion to a positively charged electrode is mediated by specifically adsorbed bromide ions. Keywords: SERS; monoprotonated pyrazine cation, silver electrode, pyrazinium.

Electrochemical processes involving pyrazine (pz) and monoprotonated pyrazine cation (pzH(+)) adsorbed on a silver surface have been investigated by Surface-Enhanced Raman Scattering (SERS). The investigation of the faradaic and non-faradaic behaviour of pz adsorbed on silver by SERS is a good example of the application of this technique to the study of solid-liquid interfaces. Electrochemical SERS can be used to infer the orientation of the adsorbed molecule. The results presented in this work indicate that pz adsorbs end-on via the lone pair electrons on the nitrogen, and this orientation is not potential dependent. On the other hand, the pzH(+) adsorption mode does change with potential. A flat adsorbed cation is predominant at potentials more negative than -300 mV. The end-on adsorbed pzH(+) dominates the SERS spectrum at potentials more positive than -170 mV. Electrochemical SERS is also useful for the in situ study of faradaic processes. The electroreduction of pz was observed at potentials more negative than - 900 mV, and the reduction product was identified as the 1,4-dihydropyrazine cation (DHPz(+)).

Chronocoulometry and Raman spectroscopy have been applied to study pyrazine adsorption at the Au(210) electrode surface. The adsorption isotherms, Gibbs energies of adsorption, and the electrosorption valency for pyrazine adsorption at the Au(210) electrode surface have been determined. Surface-enhanced Raman Scattering (SERS) spectra of pyrazine adsorbed on an "unroughened" Au(210) electrode surface have been obtained for the first time. The thermodynamic data and the SERS spectra indicate that pyrazine adsorbs on the Au(210) electrode via the nitrogen lone pair (N-bonded configuration) over the whole range of electrode potentials investigated. Consequently, the pyrazine molecule assumes only the vertical orientation at this surface of gold. The adsorption of pyrazine at the Au(210) and Au(111) surfaces is compared and the influence of the surface crystallography on the adsorption of this molecule at gold electrodes is discussed. Keywords: adsorption at Au(210), pyrazine, SERS, chronocoulometry.

The Raman non-coincidence effect (NCE) of the carbonyl stretching band of methyl formate diluted in acetonitrile was studied. The observed NCE was compared with the predictions of a number of models for non-isotopic dilutions. All of the models failed. Thermodynamic data indicate that the mixtures are very nearly ideal. The failures of the models, therefore, cannot be solely ascribed to the assumption of solution ideality. The carbonyl bandwidths were also measured and their behaviour was unusual (first increasing and then decreasing), although consistent with previous findings for isotopic dilutions. © 1998 John Wiley & Sons, Ltd.

Surface enhanced Raman scattering (SERS) has been used to study the electrochemical reduction of CO2 on the copper electrode surface. The effect of different oxidation reduction cycles (ORCs) on the observed SERS has been investigated. A modification of the ORCs has been used to create sites which provide stable SERS, allowing exploration of the mechanism of CO2 reduction. The experimental conditions required to observe SERS in this system are described. The time-dependent decay of the SERS bands and the time-dependent increase of a new band, attributed to the formation of a poisoning species, have been measured the intermediate species is CO2 the poisoning species is a copper oxide patina.

The electrochemical reduction of pyrazine (pz) on a silver electrode from a 1.0 M KBr solution has been investigated by surface enhanced Raman scattering (SERS). New bands from products of reduced pyrazine were observed at potentials more negative than -900 mV (vs. SCE). The main product is believed to be the 1,4-dihydropyrazine cation (DHPz(+)). The reduction is not completly reversible. It is clear from the observed spectroscopic and electrochemical data that some of the DHPz(+) was not re-oxidized when the potential scan was switched to positive values. This DHPz(+) (or one of its derivatives with similar structure) remained trapped on the electrode surface even at potentials more positive than the point of zero charge (pzc) of silver in this medium. It is proposed that the cation binds to adsorbed halide at potentials more positive than the pzc. The presence of reduced pyrazine products at potentials more positive than the pzc can lead to misinterpretations of the SER spectrum of pyrazine.

Surface-enhanced Raman scattering (SERS) spectra of pyrazine and pyridine adsorbed on an "unroughened" Au(210) electrode surface have been obtained for the first time. The SERS spectra indicate that both pyridine and pyrazine adsorb on the Au(210) electrode via their nitrogen lone pairs (end-on configuration). The integrated SERS intensities from the ring-breathing vibrations (ca. 1010 cm-1 for pyridine and 1019 cm-1 for pyrazine) were measured. The potential profiles (integrated SERS intensity versus potential plots) were compared to the surface coverage data, obtained electrochemically, for the adsorption of pyridine and pyrazine on Au(210). No simple relationship was found between the SERS intensities and the surface coverage data; however, it seems that the SERS intensities track the surface coverage for low surface concentrations (less than a monolayer).

Surface enhanced Raman scattering (SERS) spectra of pyrazine (pz) adsorbed on a silver electrode from aqueous solutions containing either 1.0 M KCl or 1.0 M KBr are presented. The SER spectra display bands which are usually forbidden in the normal Raman spectrum of pz. The presence of these forbidden bands and the orientation of the molecules on the electrode surface are discussed under the two most accepted surface enhancement theories: the charge transfer and the electromagnetic model. The dependence of SERS intensity of several pz vibrational modes on the applied potential (potential profile) is also presented for different pz concentrations and excitation wavelengths. SER spectra, obtained at potentials more negative than −900 mV (vs. SCE), contain new bands due to reduction of the pz molecule. It is clear that some of these products of decomposed pz remain trapped on the electrode surface, and this can lead to misunderstandings of the interpretation of the adsorbed pz spectrum. Several controversial aspects presented in the literature about the surface Raman spectrum of pz are clarified and discussed.

Raman spectra of the hydrogen-deuterium exchange reaction occurring in the HCOO−-D2O system at elevated temperatures and pressures are reported. The rate constants at four temperatures have been measured and from these an activation energy of around 170 kJ mol−1 has been calculated. Exchange also takes place in the DCOO−-H2O system. The rate constants at four temperatures indicate an activation energy of 93 kJ mol−1.

The species in the electrolyte and at, or near, the working electrode surface of an operating cell can be identified by Raman spectroscopy. Examples for the electrolyte methyl acetate/LiAsF6, without and with CO2 saturation, are described. The role of the additive, tetramethylammonium, is suggested. Conclusions from measurements of corrosion potential-time transients following in situ cutting to expose bare lithium metal to various organic electrolyte environments are reviewed. Preliminary Raman spectral measurements of carbon-coke anodes suggest that charging cycles cause intraplanar rupturing, thus reducing the microcrystallite size and causing measurable disorder.