J. Corset

Raman spectra of electrochemically prepared silver surfaces and silver halide layers. Protonation of pyridine by adsorbed water

The Raman spectra of Ag/AgX interfaces (X = Cl, Br, 1) show that either through electrochemical oxidation or through photochemical effect (Ago)n and X2− or Ago…X2− species are formed as defects in the colloidal AgX layer. These species are probably stabilized through water salvation. It is demonstrated that this adsorbed water is responsible for the observed protonation of pyridine when adsorbed from the gas phase on such surfaces.

Etude de la structure de carbanions en α du soufre

Abstract Carbanions α to sulfoxides and sulfones C 6 H 5 S(O)nCH 2 M (n  1, 2; M  Li or K) have been studied by infrared and Raman spectroscopy. A strong increase of the force constant of the SCH 2 M bond, and a similar decrease of that of the SO bond(s) are observed. This implies that the negative charge is delocalized over the carbon and oxygen atoms. 1 H NMR shows that carbanions α to sulfoxides are configurationally stable at low temperature. The interconversion energy depends on the polarizing ability of the counter-ion (Li + : Δ G 13.6 kcal mol -1 ; K + : Δ G 10.7 kcal mol -1 ). The coupling constant of the methylenic hydrogens ( J AB 2 Hz) confirms the nearly planar configuration of the anionic carbon in the α metallated sulfoxides.

Diffuse Reflectance Infrared Spectroscopy: Experimental Study of Nonabsorbing Materials and Comparison with Theories:

This work presents a comprehensive study of the diffuse reflectance of nonabsorbing powders in the mid-infrared. The changes in the optical and physical parameters of the powder (particle size, granulometric distribution, powder density, refractive index) have been used to get a better understanding of the influence of each parameter on the diffusely reflected intensity, as well as the mechanisms of the light diffusion by the powder. A commercial diffuse reflectance attachment has been tested optically for the accuracy of measurements, the focalization of the incident beam at the sample surface being taken into account. The experimental results have been compared to results of existing diffusion theories. This comparison proves the pertinency of the observed variation of the intensity of the diffusely reflected light with the refractive index which increases from 0 for n = 1 to a maximum and then decreases with n. This behavior is related to the anisotropy of the light diffusion both at the inside and then at the outside of the particles and to the light trapping by total reflection inside the particles.

Diffuse reflectance infrared spectroscopy: an experimental measure and interpretation of the sample volume size involved in the light scattering process

This work presents the second part of a basic study of diffuse reflectance spectroscopy through a comparison of experimental observations with existing theories of diffuse reflectance of non-absorbing powders. The diffusion volume approximate shape has been assumed to be a cylinder. Its dimensions have been measured for different non-absorbing powders with a refractive index from 1.4 to 3.4, and with different distributions of particle size larger than the wavelength. The lateral extension diameter Φm of this volume is at least two times larger than that of the irradiated sample surface. The variation of the cylinder height corresponding to the penetration depth, z∞, has a behavior opposite to that of the powder diffusion coefficient, S. Its variation with the mean particle diameter is smaller than predicted by the theories. For KBr, a 1 mm thick layer can be considered as a semi-infinite layer. Comparison between existing theories of diffuse reflectance of powdered samples, shows that the statistical theories explain a good deal of the experimental observations concerning their variation with the particle parameters. This comparison shows a similarity between attenuated total reflection and diffuse reflectance spectra. Nevertheless, some discrepancies still persist; this may be due to the fact that the side-way scattering, which may be related to light transfer between neighbouring rough particles by frustrated total reflection, has only been indirectly taken into account.

Vibrational study and molecular structure of two S4 isomers in sulphur vapour

Raman spectra of sulphur vapour for two pressures (0.1 and 0.2 MPa) and various temperatures up to 700 °C were recorded using several krypton ion and argon ion laser exciting radiation wavelengths. Resonance Raman enhancement effects in conjunction with 32S/34S isotopic effects allow one to distinguish three fundamental vibrational modes (νs, νc, δs) of a green absorbing (λmax = 530 nm) chain-like S4 molecule from the modes belonging to S3 and other cyclic S6, S7 and S8 molecules. Moreover, using a 647.1 nm excitation wavelength, several vibrational modes of another red absorbing (λmax = 560–660 nm) branched-ring S4 isomer were characterized. Finally, normal coordinate treatments confirm the trans planar C2h structure of the chain-like S4 species, whereas a comparison of the observed and calculated wavenumbers for the red absorbing S4 isomer is in agreement with a branched-ring structure. Copyright

Etude comparée par spectrométrie de vibration de sulfures, sulfoxydes et sulfones organiques—II. Méthyl phényl-sulfure, méthyl phényl-sulfoxyde et méthyl phényl-sulfone hydrogènes et deutériés. Champ de force de valence, modes normaux de vibration

Resume The infrared and Raman spectra of methyl phenyl-sulfide, -sulfoxide and -sulfone, and deuterated either on the aromatic ring or on the methyl group, are reported and their assignment discussed. From the data obtained for the methyl phenyl-sulfide a valence force field has been refined for the C 6 H 5 S aromatic ring, this force field being transferrable to the sulfoxide and sulfone. This force field and those preceedingly obtained for dimethyl compounds have been transferred and adjusted to the observed frequencies of the methyl phenyl-sulfoxide and sulfone. The potential energy distributions of the normal modes are discussed. The main force constants of the bonds around sulfur are compared with those obtained for the dimethyl compounds. The influence of the oxidation state of the sulfur observed for the dimethyl compounds is also found in the methyl phenyl compounds. The comparison of the k (CS) force constants shows a slight electron delocalization towards the phenyl ring. While for the sulfide and sulfoxide the delocalization only takes place along the CSC group, in the sulfone the effects is partly compensated by a stronger conjugation of the oxygen lone pairs.

Vibrational spectra and possible conformers of dimethylmethylphosphonate by normal mode analysis

Abstract A careful assignment of the i.r. and Raman spectra of CH 3 P(O)(OCH 3 ) 2 , CD 3 P(O)(OCH 3 ) 2 , CH 3 P(O)(OCD 3 ) 2 and CD 3 P(O)(OCD 3 ) 2 and a comparison with those of the parent molecules CH 3 OP(O)Cl 2 and CD 3 OP(O)Cl 2 suggest that only one conformer exists in the liquid state. This conformer is probably close to the most stable one calculated by CNDO/2 and ab initio STO-3G methods, with one CH 3 O group trans and the other cis to the PO group. The characteristic modes of the CP(O)(OC) 2 skeleton are analysed through a force field calculation. It is shown that the stretching vibrations of the single bonds PC and PO are strongly coupled. As already observed for carboxylic esters, it is shown that only mixed skeletal modes and mostly the bending modes are sensitive to the conformation of the methoxy groups around the PO single bond. On the other hand the v (PO) mode does not vary for the different conformers, and the extra components appearing in its vicinity, as well as in that of the v (PC) main vibrational mode, are best understood as being due to Fermi resonances with harmonic or combination tones coupling with these modes.

STRUCTURAL STUDY OF CARBANIONIC SPECIES FROM BIS(DIETHOXYPHOSPHONYL)-METHANE BY IR, RAMAN AND 1H, 31P, 13C NMR SPECTROSCOPIES

Abstract An IR and Raman study of the lithium associated carbanionic species 1 formed from bis(diethoxyphosphonyl)-methane in the solid state and in THF solution, as well as the IR and 1H, 31P, 13C NMR study of the potassium associated one in pyridine and dimethylsulfoxide are reported. A chelated symmetrical structure exists in the solid state and in associating medium. The central carbon is planar or nearly so from the NMR data. However, the negative value of 2 J PH in the anionic species raises the problem of estimating the various factors involved in the two bond coupling constants.

SERS study of pyridine vapor exposed to silver substrates electrochemically prepared.

Abstract Silver electrodes, previously prepared in KCl, KBr and KNO 3 electrolyte solutions, are exposed to a saturated vapor of pyridine, at room temperature. Surface complexes involving a silver halide and pyridine are detected during the gas - solid interaction. A low frequency band was observed, without exposure to pyridine, when a large amount of silver halide deposited on the electrode, is irradiated with a laser blue line. Photoreduction of the silver halide into metal aggregates occurs during the exposure to the laser. Some hypothesis about the adsorption of pyridine at room temperature are advanced from results obtained with a silver electrode prepared in a KNO 3 solution.

Etude comparée par spectrométrie de vibration de sulfures, sulfoxydes et sulfones organiques—I. Sulfures, sulfoxydes et sulfones diméthyles

Abstract A valence force field has been evaluated for dimethylsulfone from data in the literature (after revision of some assignments) with the same assumptions as those of Forel et al. on dimethylsulfide and dimethylsulfoxide. On this basis, a comparison is made between the bonds changes around the sulfur atoms and its oxidation state. The increase of the k(CS) force constant in the sulfur and the sulfone compared to sulfoxide is explained by a change in the hybridation of the sulfur atom orbitals between the sulfone on the one hand and the sulfur and the sulfoxyde on the other.