Dissociative electron attachment to dinitrogen pentoxide, N2O5

Electron attachment was studied in gaseous dinitrogen pentoxide, N2O5, for incident electron energies between a few meV and 10 eV. No stable parent anion N2O5- was observed but several anionic fragments (NO3-, NO2-, NO-, O-, and O-2(-)) were detected using quadrupole mass spectrometry. Many of these dissociative pathways were found to be coupled and provide detailed information on the dynamics of N2O5 fragmentation. Estimates of the cross sections for production of each of the anionic fragments were made and suggest that electron attachment to N2O5 is amongst the most efficient attachment reactions recorded for nonhalogenated polyatomic systems. (C) 2004 American Institute of Physics.

Chalcogenide-halides of niobium (V). 1. Gas-phase structures of NbOBr3, NbSBr3, and NbSCl3. 2. Matrix infrared spectra and vibrational force fields of NbOBr3, NbSBr3, NbSCl3, and NbOCl3

The molecular structures of NbOBr3, NbSCl3, and NbSBr3 have been determined by gas-phase electron diffraction (GED) at nozzle-tip temperatures of 250 degreesC, taking into account the possible presence of NbOCl3 as a contaminant in the NbSCl3 sample and NbOBr3 in the NbSBr3 sample. The experimental data are consistent with trigonal-pyramidal molecules having C-3v symmetry. Infrared spectra of molecules trapped in argon or nitrogen matrices were recorded and exhibit the characteristic fundamental stretching modes for C-3v species. Well resolved isotopic fine structure (Cl-35 and Cl-37) was observed for NbSCl3, and for NbOCl3 which occurred as an impurity in the NbSCl3 spectra. Quantum mechanical calculations of the structures and vibrational frequencies of the four YNbX3 molecules (Y = O, S; X = Cl, Br) were carried out at several levels of theory, most importantly B3LYP DFT with either the Stuttgart RSC ECP or Hay-Wadt (n + 1) ECP VDZ basis set for Nb and the 6-311 G* basis set for the nonmetal atoms. Theoretical values for the bond lengths are 0.01-0.04 Angstrom longer than the experimental ones of type r(a), in accord with general experience, but the bond angles with theoretical minus experimental differences of only 1.0-1.5degrees are notably accurate. Symmetrized force fields were also calculated. The experimental bond lengths (r(g)/Angstrom) and angles (angle(alpha)/deg) with estimated 2sigma uncertainties from GED are as follows. NbOBr3: r(Nb=O) = 1.694(7), r(Nb-Br) = 2.429(2), angle(O=Nb-Br) = 107.3(5), angle(Br-Nb-Br) = 111.5(5). NbSBr3: r(Nb=S) = 2.134(10), r(Nb-Br) = 2.408(4), angle(S=Nb-Br) = 106.6(7), angle(Br-Nb-Br) = 112.2(6). NbSCl3: Nb=S) = 2.120(10), r(Nb-Cl) = 2.271(6), angle(S=Nb-Cl) = 107.8(12), angle(Cl-Nb-Cl) = 111.1(11).

Hydrolysis of N2O5 on sub-micron mineral salt aerosols

The kinetics of reactive uptake of gaseous N2O5 on sub-micron aerosol particles composed of aqueous ammonium sulfate, ammonium hydrogensulfate and sodium nitrate has been investigated. Uptake was measured in a laminar flow reactor, coupled with a differential mobility analyser (DMA) to obtain the aerosol size distribution, with N2O5 detection using NO chemiluminescence. FTIR spectroscopy was used to obtain information about the composition and water content of the aerosol particles under the conditions used in the kinetic measurements. The aerosols were generated by the nebulisation of aqueous salt solutions. The uptake coefficient on the sulfate salts was in the range [gamma]=0.0015 to 0.033 depending on temperature, humidity and phase of the aerosol. On sodium nitrate aerosols the values were much lower, [gamma]<0.001, confirming the inhibition of N2O5 hydrolysis by nitrate ions. At high humidity (>50% r.h.) the uptake coefficient on liquid sulfate aerosols is independent of water content, but at lower humidity, especially below the efflorescence point, the reactivity of the aerosol declines, correlating with the lower water content. The lower uptake rate on solid aerosols may be due to limitations imposed by the liquid volume in the particles. Uptake on sulfate aerosols showed a negative temperature dependence at T>290 K but no significant temperature dependence at lower temperatures. The results are generally consistent with previous models of N2O5 hydrolysis where the reactive intermediate is NO2+ produced by autoionisation of nitrogen pentoxide in the condensed phase.

Dissociative electron impact ionization of N2O5

Electron impact ionization of dinitrogen pentoxide for incident electron energies up to about 25 eV has been investigated by use of a crossed beams quadrupole mass spectrometer system. The experiments reported in this paper detected the fragmentation products NO2+, NO+, O+, N+, and NO3+. No stable N2O5+ ion was observed. The NO3+ fragment, for which we determine an appearance energy 13.25 +/- 0.30 ev, has not been observed previously. This appearance energy is close to the calculated threshold.

Film-forming polymers containing in the main-chain dibenzo crown ethers with aliphatic (C-10-C-16), aliphatic-aromatic, or oxyindole spacers

Novel, linear, soluble, high-molecular-weight, film-forming polymers and copolymers in which main-chain crown ether units alternate with aliphatic (C-10-C-16) units have been obtained for the first time from aromatic electrophilic substitution reactions of crown ethers by aliphatic dicarboxylic acids followed by reduction of the carbonyl groups. The crown ether unit is dibenzo-18-crown-6, dibenzo-21-crown-7, dibenzo-24-crown-8, or dibenzo-30-crown-10; the aliphatic spacer is derived from a dicarboxylic acid (sebacic, 1,12-dodecanedicarboxylic, hexadecanedioic or 1,4-phenylenediacetic acids). The reactions were performed at 35 degrees C in a mixture of methanesulfonic acid (MSA) with phosphorus pentoxide, 12:1 (w/w), (Eaton's reagent). The carbonyl groups in the polyketones obtained were completely reduced to methylene linkages by treatment at room temperature with triethylsilane in a mixture of trifluoroacetic acid and dichloromethane. Polymers containing in the main chain crown ethers alternating with oxyindole fragments were prepared by one-pot condensation of crown ethers with isatin in a medium of Eaton's reagent. A possible reaction mechanism is suggested. According to IR and NMR analyses, the polyacylation reactions lead to the formation of isomeric (syn/anti-substituted) crown ether units in the main chain. The polymers obtained were soluble in the common organic solvents, and flexible transparent films could be cast from the solutions. DSC and X-ray studies of the polymers with "symmetrical" crown ethers reveal the presence of the endotherms corresponding to the supramolecular assemblies.

Thermoelectric properties of TiS2 mechanically alloyed compounds

Bulk polycrystalline samples in the series Ti1−xNbxS2 (0 ≤ x ≤ 0.075) were prepared using mechanical alloying synthesis and spark plasma sintering. X-ray diffraction analysis coupled with high resolution transmission electron microscopy indicates the formation of trigonal TiS2 by high energy ball-milling. The as-synthesized particles consist of pseudo-ordered TiS2 domains of around 20–50 nm, joined by bent atomic planes. This bottom-up approach leads, after spark plasma sintering, to homogeneous solid solutions, with a niobium solubility limit of x = 0.075. Microstructural observations evidence the formation of small crystallites in the bulk compounds with a high density of stacking faults. The large grain boundary concentration coupled with the presence of planar defects, leads to a substantial decrease in the thermal conductivity to 1.8 W/mK at 700 K. This enables the figure of merit to reach ZT = 0.3 at 700 K for x = 0.05, despite the lower electron mobility in mechanically alloyed samples due to small crystallite/grain size and structural defects.