Pierre Archirel

Bond formation between positively charged species. Non-adiabatic analysis and valence-bond model in the CO2+ case

Abstract Ab initio MCSCF calculations of the potential energy curves of the first low-lying states of the CO 2+ dication have been performed. A localization procedure of MCSCF orbitals allows us to discuss the bond formation in the framework of valence-bond theory. The non-adiabatic curves corresponding to C + + O + , C 2+ + O and C + O 2+ are described using both orthogonal and non-orthogonal quasi-atomic orbitals, allowing us to re-examine the currently proposed models of bond formation between positively charged species.

Influence of the chemical functionalities of a molecularly imprinted conducting polymer on its sensing properties: electrochemical measurements and semiempirical DFT calculations.

Starting from thiophene-based functional monomers (FM), namely, TMA, TAA, TMeOH, EDOT, and Th, bonded to atrazine (ATZ) target molecules into FM/ATZ prepolymerization dimers in acetonitrile solutions, differently functionalized molecularly imprinted conducting polymers (FM-MICP) are electrosynthesized and then washed and used as sensitive layers for ATZ recognition. Sensitivity of these layers toward ATZ, which is quantified by cyclic voltammetric measurements, decreases in the following order of functional monomers: TMA, TAA, TMeOH, EDOT, and Th. Absolute values of the FM-ATZ dimerization free energies are calculated with the help of DFT/PCM calculations and of an empirical correction of the entropy effects, using a modified Wertz formula. A strong correlation is found between FM-MICP sensitivity and the amount of FM/ATZ prepolymerization complexes.

Potential energy surfaces for the (ArCO)+ system

The five lowest doublet potential energy surfaces for the (ArCO)+ system have been determined using the procedure of Archirel and Levy. These states correlate at infinite separation, in order of increasing energy, to Ar+CO+(X 2Σ+), Ar+(2P3/2)+CO, Ar+(2P1/2)+CO, and Ar+CO+(A 2Π). The potential energy curves are shown at several values of the orientation angle. In addition, contour maps of the two lowest surfaces are presented. Both of these surfaces are quite anisotropic, and each has a deep potential well. Adiabatic vibronic potential energy surfaces have also been computed. These give insight into the charge transfer process at low collision energies. For the purpose of comparison the five lowest surfaces for the isoelectronic system (ArN2)+ are also shown.

Molecular dynamics simulations of the Ag+ or Na+ cation with an excess electron in bulk water

The properties of an excess electron interacting with a monovalent cation in bulk water are studied by molecular dynamics simulations. Sodium and silver cations are chosen as prototypical cases because of their very different redox properties. In both cases, mixed quantum classical molecular dynamics simulations reproduce the experimental UV-Vis spectra. In the case of silver, we observe a highly polarized neutral atom, corresponding to a dipolar excitonic state. For sodium a contact cation/electron pair is observed. Free energy curves along the cation electron coordinate are calculated using quantum Umbrella Sampling technique. The relative stability of the different chemical species is discussed.

Surface hopping trajectory calculations for electronic rotational and vibrational inelastic collisions for the Na-N2 system

Abstract The processes Na( 2 P) + N 2 [ 2 Σ( v, j )] Na( 2 S) + N 2 [ 2 Σ( v′, j′ )] have been investigated by classical trajectory calculations on the three lowest potential surfaces of the system Na-N 2 . The transition probabilities at the real and avoided crossings were determined according to the linear model. The coupling matrix elements for rotation of the quasimolecule NaN 2 were calculated with the aid of the Hellmann-Feynman theorem and those for the relative movement of the three atoms were extracted from the splitting of the adiabatic potential surfaces according to the Landau-Zener model. The total and differential cross sections for the quenching, the excitation and the elastic processes are in good agreement with experiment. The detailed theoretical results give a better understanding of the mechanism of the processes.

Preoptimised VB: a fast method for the ground and excited states of ionic clusters I. Localised preoptimisation for (ArCO)+, (ArN2)+ and N4+

Abstract We show that in the simple case of van der Waals ionic clusters, the optimisation of orbitals within VB can be easily simulated with the help of pseudopotentials. The procedure yields the ground and the first excited states of the cluster simultaneously. This makes the calculation of potential energy surfaces for tri- and tetraatomic clusters possible, with very acceptable computation times. We give potential curves for (ArCO) + , (ArN 2 ) + and N 4 + . An application to the simulation of the SCF method is shown for Na + H 2 O.

UV−Visible Absorption Spectra of Small Platinum Carbonyl Complexes and Particles: A Density Functional Theory Study

We investigate the influence of a carbonyl coating on the UV-visible absorption of platinum complexes and particles with the TDDFT method. We first investigate the Chini clusters [Pt(3)(CO)(6)](n)(2-), n = 1-4, for which the absorption spectra are known. We show that PBE is realistic but displays convergence issues and that B3LYP overestimates intertriangle distances and absorption intensities. We discuss the structure of the spectra and the parallel vs perpendicular character of the transition dipole with respect to the stacking axis. We then investigate the spectra of model carbonylated platinum particles: [Pt(13)(CO)(12)](2-) (with only terminal carbonyls) and [Pt(13)(CO)(24)](2-) (with only bridging carbonyls). B3LYP proves much more realistic than in the case of Chini clusters. The influence of the morphology of the platinum particle and of the carbonyl coating on the absorption spectra is discussed. The results suggest an interpretation of a spectrum, recorded in a recent synthesis.

Double-core ionization and excitation above the sulphur K-edge in , and

Experimental and theoretical results are reported on double-core excitation and ionization processes in some sulphur containing molecules. X-ray absorption spectra have been recorded at the sulphur K-edge using synchrotron radiation delivered by the DCI ring at LURE (Orsay, France). Absolute x-ray absorption cross sections have been determined for gas phase , and molecules in the 2400 - 2800 eV region. Several narrow features are observed far from the edge and assigned to double-core excited states. Two series of states are present corresponding to the triplet and singlet configurations, due to the core 1s - 2p exchange term. The energy, width and intensity of the features are strongly molecule dependent. In the case of , a theoretical determination of all the single- and double-core vacancy ionization potentials has been performed using a new theoretical approach which makes it possible to solve the convergence problem inherent in a simple SCF calculation. Results compare favourably with available experimental values. In particular, the singlet - triplet separation is correctly predicted for all the double-core ionized states. The relation between the double-core relaxation energies and the associated single-core relaxation values is discussed. Finally, the double-core excited state energies are determined within a Z + 2 core equivalent model, allowing a full assignment of the experimental spectra of .

Electron-induced growth mechanism of conducting polymers: a coupled experimental and computational investigation.

Pulse radiolysis was used to study the mechanism of HO(•)-induced polymerization of poly(3,4-ethylenedioxythiophene), PEDOT, in aqueous solution. A step-by-step mechanism has been found which involves a recurrent oxidation process by HO(•) hydroxyl radicals produced by water radiolysis. Furthermore, the cation radical, EDOT(•)(+), has been proposed as the promoter of the first step of polymerization. The determination of rate constants values and the attribution of transient and stable species were confirmed by molecular simulations and spectrokinetic analysis. Moreover, applying a series of electron pulses enabled in situ PEDOT polymerization. These polymers, which were characterized in solution or after deposition, form globular self-assembled structures with interesting conducting properties. Such a synthesis initiated for the first time by an electron accelerator gives us a glimpse of future promising industrial applications in the field of conducting polymers synthesis.

Oxidation of Bromide Ions by Hydroxyl Radicals: Spectral Characterization of the Intermediate BrOH•–

The reaction of (•)OH with Br(-) has been reinvestigated by picosecond pulse radiolysis combined with streak camera absorption detection and the obtained spectro-kinetics data have been globally analyzed using Bayesian data analysis. For the first time, the absorption spectrum of the intermediate species BrOH(•-) has been determined. This species absorbs in the same spectral domain as Br(2)(•-): the band maximum is roughly at the same wavelength (λ(max) = 352 nm instead of 354 nm) but the extinction coefficient is smaller (ε(max) = 7800 ± 400 dm(3) mol(-1) cm(-1) compared with 9600 ± 300 dm(3) mol(-1) cm(-1)) and the band is broader (88 nm versus 76 nm). Quantum chemical calculations have also been performed and corroborate the experimental results. In contrast to Br(2)(•-), the existence of several water-BrOH(•-) configurations leading to different transition energies may account for the broadening of the absorption spectrum in addition to the higher number of degrees of freedom.