Didier Begue

As the prototype Curtius rearrangement reaction, carbamoyl azide decomposes into aminoisocyanate and molecular nitrogen. However, the key intermediate carbamoylnitrene was previously undetected, even though the decomposition of carbamoyl azides has been studied frequently since its discovery in the 1890s. Upon ArF laser (λ=193 nm) photolysis, the stepwise decomposition of the two simplest carbamoyl azides H2 NC(O)N3 and Me2 NC(O)N3, isolated in solid noble gas matrices, occurs with the formation of the corresponding carbamoylnitrenes H2 NC(O)N and Me2 NC(O)N. Both triplet species are characterized for the first time by combining matrix-isolation IR spectroscopy and quantum-chemical calculations. Subsequent visible-light irradiations cause efficient rearrangement of these nitrenes into the respective aminoisocyanates.

In this paper we present a new vibrational configuration interaction method known as a parallel vibrational multiple window configuration interaction P_VMWCI which generates several VCI matrices and enables the variational treatment of medium size molecular systems. Application to acetaldehyde gives a new interpretation of the MIR experimental data.

Electrostatic interaction schemes have been applied to predict the evolution of the polarizability in Sin clusters of increasing size (n =3-19). Both on-site polarization and charge transfer effects have been included in the interaction scheme, of which the values have been compared to B3LYP/6-311G∗ and other first principles results. To reproduce the pattern of the variation of the B3LYP average polarizability per Si atom as a function of the cluster size, the atomic polarizability employed in the interaction scheme should amount to roughly 80% of the bulk atomic polarizability. However, this results in a systematic underestimation of the polarizability per Si atom by about 25%, whereas increasing the atomic polarizability value leads to excessive variations of the polarizability per Si with the cluster size. An improved agreement is obtained when incorporating a charge transfer contribution, at least for sufficiently large clusters, substantiating the fact that in large clusters electrostatic effects are dominant over quantum effects. This charge transfer atomic polarizability term has been modeled by a simple function, which evolves linearly with the difference of Cartesian coordinates between the atom and the center of mass and that has been verified using B3LYP/6-311G∗ calculations. In the case of the prediction of the polarizability anisotropy, a similar atomic polarizability corresponding to 80% of the bulk atomic polarizability has been shown suitable to reproduce the B3LYP results, whereas inclusion of charge transfer effects can slightly improve the agreement, provided the amount of charge transfer increases with the size of the cluster.

Di(oxymethylene)glycol forms in formaldehyde aqueous solutions by polymerization of methanediol. The structure and hydrogen bond interactions of di(oxymethylene)glycol with water were characterized by performing Car-Parrinello molecular dynamics simulations. The anharmonic vibrational frequencies of di(oxymethylene)glycol in solution were determined with ab initio calculations considering explicitly the hydrogen-bonded water molecules, while other interactions with solvent were described within a polarizable continuum model approach. The calculations allow for a detailed interpretation of the experimental Raman spectrum of formaldehyde aqueous solutions, leading to the assignment of the band at 920 cm(-1) to the symmetric CO stretching mode of di(oxymethylene)glycol.

The complex organic material that is found on the surface and within the haze layer of Titan is attributed to chemistry occurring in its thick N2/CH4 atmosphere. Although several groups are producing in various laboratory setting the socalled tholins which have been investigated by using analytical methods including UV/Vis, fluorescence, IR, and MS1-5, these very complex organic mixtures still hold many unanswered questions, especially related to the potentiality for their prebiotic chemistry. In addition to tholins characterization and analysis, we recently investigated quantitatively the hydrolysis kinetics of tholins in pure and NH3 containing water at different temperatures.7-8 Our groups at UJF (Grenoble) and at U of Arizona (Tucson) have been collaborating on mass spectral analyses of tholins samples for several years.9 Here, we report our most recent results on the structural characterization of tholins by infrared multiphoton dissociation (IRMPD) action spectroscopy10 and ul...

ABSTRACT Large-scale introduction of Organic Solar Cells (OSCs) onto the market is currently limited by their poor stability in light and air, factors present in normal working conditions for these devices. Thus, great efforts have to be undertaken to understand the photodegradation mechanisms of their organic materials in order to find solutions that mitigate these effects. This study reports on the elucidation of the photodegradation mechanisms occurring in a low bandgap polymer, namely, Si-PCPDTBT (poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,5′-diyl]). Complementary analytical techniques (AFM, HS-SPME-GC-MS, UV-vis and IR spectroscopy) have been employed to monitor the modification of the chemical structure of the polymer upon photooxidative aging and the subsequent consequences on its architecture and nanomechanical properties. Furthermore, these different characterization techniques have been combined with a theoretical approach based on quantum chemistry to elucidate the evolution of the polymer alkyl side chains and backbone throughout exposure. Si-PCPDTBT is shown to be more stable against photooxidation than the commonly studied p-type polymers P3HT and PCDTBT, while modeling demonstrated the benefits of using silicon as a bridging atom in terms of photostability.

... XXXI 99 Huron B, Rancurel P and Malrieu JP 1973 J. Chem. Phys. 58 5743 Kobayashi R, Koch H, Jorgensen P and Lee TJ 1993 Chem. Phys. Lett. 211 94 Koch H and Harrison R 1991 J. Chem. Phys. 95 7479 Maeder F and Kutzelnigg W 1979 Chem. Phys. 42 95 Marino MM ...

The present study is aimed at a detailed analysis of supercritical water structure based on the combination of experimental vibrational spectra as well as molecular modeling calculations of isolated water clusters. We propose an equilibrium cluster composition model where supercritical water is considered as an ideal mixture of small water clusters (n=1-3) at the chemical equilibrium and the vibrational spectra are expected to result from the superposition of the spectra of the individual clusters, Thus, it was possible to extract from the decomposition of the midinfrared spectra the evolution of the partition of clusters in supercritical water as a function of density. The cluster composition predicted by this model was found to be quantitatively consistent with the near infrared and Raman spectra of supercritical water analyzed using the same procedure. We emphasize that such methodology could be applied to determine the portion of cluster in water in a wider thermodynamic range as well as in more complex aqueous supercritical solutions.

Electrostatic interaction schemes have been applied to predict the evolution of the polarizability in Si(n) clusters of increasing size (n=3-19). Both on-site polarization and charge transfer effects have been included in the interaction scheme, of which the values have been compared to B3LYP/6-311G(*) and other first principles results. To reproduce the pattern of the variation of the B3LYP average polarizability per Si atom as a function of the cluster size, the atomic polarizability employed in the interaction scheme should amount to roughly 80% of the bulk atomic polarizability. However, this results in a systematic underestimation of the polarizability per Si atom by about 25%, whereas increasing the atomic polarizability value leads to excessive variations of the polarizability per Si with the cluster size. An improved agreement is obtained when incorporating a charge transfer contribution, at least for sufficiently large clusters, substantiating the fact that in large clusters electrostatic effects are dominant over quantum effects. This charge transfer atomic polarizability term has been modeled by a simple function, which evolves linearly with the difference of Cartesian coordinates between the atom and the center of mass and that has been verified using B3LYP/6-311G(*) calculations. In the case of the prediction of the polarizability anisotropy, a similar atomic polarizability corresponding to 80% of the bulk atomic polarizability has been shown suitable to reproduce the B3LYP results, whereas inclusion of charge transfer effects can slightly improve the agreement, provided the amount of charge transfer increases with the size of the cluster.

Both experimental and theoretical investigations are reported on the infrared spectrum of vinylphosphine-borane (CH(2)=CHPH(2) x BH(3)), a donor-acceptor complex. The gas phase infrared spectra (3500-600 cm(-1)) have been recorded at 0.5 cm(-1) resolution. This first primary alpha,beta-unsaturated phosphine-borane synthesized up to now is kinetically very unstable in the gas phase and decomposes rapidly into two fragments: the free vinylphosphine CH(2)=CHPH(2) and the monoborane BH(3) which dimerizes to form the more stable diborane B(2)H(6). Spectra of free CH(2)=CHPH(2) and B(2)H(6) compounds were also recorded to assign some vibration modes of the complex in very dense spectral regions. The analysis was completed by carrying out quantum mechanical calculations by density functional theory method at the B3LYP/6-31+G(**) level. Anharmonic frequencies and infrared intensities of the two predicted gauche and syn conformers of the vinylphosphine-borane complex were calculated in the 3500-100 cm(-1) region with the use of a variational approach, implemented in the P_ANHAR_V1.2 code. Because of the relatively weak interaction between the vinylphosphine and the monoborane, the vibrations of the complex can easily be subdivided into modes localized in the CH(2)=CHPH(2) and BH(3) moieties and into "intermolecular" modes. Localized modes are unambiguously correlated with the modes of the isolated monomers. Therefore, they are described in terms of the monomer vibrations, and the complexation shifts are defined as Delta nu = nu(complex) - nu(monomer) to make the effect of the complexation precise on each localized mode. In this objective, anharmonic frequencies and infrared intensities of the BH(3) monomer and the stable gauche and syn conformers of the free vinylphosphine were obtained at the same level of theory. In the gas phase, only the syn form of the complex was observed and assigned. All theoretically predicted frequencies and complexation shifts in magnitude and direction are in good agreement with experiment. By infrared spectroscopy assisted by quantum chemical calculations, the consequences of the complexation of an alpha,beta-unsaturated phosphine by borane on the physicochemical properties of the formed 12-atom complex have been efficiently evaluated.

... such as state-of-art ICP-MS, MC-ICP-MS and TIMS. The additional nomenclature to express the MIF component of the isotopic composition of Hg was introduced by Blum and Bergquist13 and is similar to the notation previously developed for MIF of oxygen and sulfur. ...

Although enamines are well-known for their ability to isomerize into the corresponding imines, the compounds containing a phosphorus or arsenic atom are much easily isolated on their enephosphine or enarsine form [1]. While vinylamine protonates preferentially at the ...