Should a franck-condon or a curve-crossing picture be applied to ion-target collisional activation? A study of keV CO<Stack><Subscript>2</Subscript><Superscript>+·</Superscript></Stack>/He collisions by emission spectroscopy

Collision-induced photon emissions (CIE) were observed for keV CO₂^+·/He collisions from 190 to 1020 nm. The emissions were assigned to the Δν=0 band of the CO₂^+· B ²Σ_u⁺ → X ²Π_g electronic transition and the Δν = +3, +2, +1, 0, −1, −2, −3 vibrational transition progression in the CO₂^+· A ²Π_u → X ²Π_g electronic transition. The other peaks arise from the emissions of excited O^· fragment atoms and the target gas. The relative intensities of the CO₂^+· and O^· emissions are independent of the ion translational energy above 3 keV, supporting the curve-crossing mechanism for collisional excitation. Investigation of the relative intensities within the A ²Π_u → X ²Π_g emission of CO₂^+· indicates that the vibrational distribution is well described by the Franck-Condon principle at high collision energy, a consequence of short collision time but not necessarily an indication of vertical transitions. Below 3 keV ion translational energy, vibrational excitation in the A ²Π_u electronic state was observed. The observation is consistent with the explanation that the reaction occurs at small impact parameters, in which short-range, repulsive interactions between the projectile and the target result in direct translational-vibrational excitation.     

Cinetique de polymerisation du trans-pentadiene-1,3

Polymerization of trans-1,3 pentadiene was first studied in relation to the ageing time of the catalytic system triethylaluminium-tetrabutylorthotitanate. The species so produced react with the monomer; the great importance of the monomer, in the initiation stage, has been shown. The apparent rate constant (kp), proportional to the number of active centres, varies inversely with the initial monomer concentration. On the contrary, the length of polymer chains as well as the 1,4 cis content are directly related to the initial monomer concentration. The life-time of chains seems to be rather great. The number of active sites is very low compared with that of titanium atoms; the hypothesis of Hirai about their nature seems to agree well with our experimental results.     

Software improvements for gas chromatography-mass spectrometry-calculator system used in the analysis of trace organic compounds from environmenta samples

Computer programs are described which have significantly increased the capabilities of a low-cost gas chromatogaphy-mass spectrometry (GC-MS)-calculator system. These programs allow storage on floppy disk of ion abundance and retention time data for the total ion current and as many as six mass chromatograms in addition to mass spectra taken at the top of eluting GC peaks. Manufacturer-supplied software was only capable of storing the mass spectra. Ion abundance data may be displayed by means of a flexible, interactive program which uses an x–y plotter. Both qualitative and quantitative analyses may be performed for selected compounds in a single GC-MS run. Examples of the use of this software in the analysis of benzene extracts of incinerator fly-ash samples are presented.     

Dioxin analysis by gas chromatography-Fourier transform ion cyclotron resonance mass spectrometry (GC-FTICRMS)

The feasibility of utilizing a gas chromatograph-tandem quadrupole-Fourier transform ion cyclotron resonance mass spectrometer (GC-MS/MS-FTICRMS) to analyze chlorinated-dioxins/furans (CDDs/CDFs) and mixed halogenated dioxins/furans (HDDs/HDFs) was investigated by operating the system in the GC-FTICRMS mode. CDDs/CDFs and mixed HDDs/HDFs could be analyzed at 50,000 to 100,000 resolving power (RP) on the capillary gas Chromatographic time scale. Initial experiments demonstrated that 1 pg of 2,3,7,8-tetrachlorodibenzop-dioxin (TCDD) and 5 pg of 2-bromo-3,7,8-trichlorodibenzo-p-dioxin (BTrCDD) could be detected. The feasibility of utilizing an FTICRMS for screening of CDDs/CDFs, HDDs/HDFs and related compounds was also investigated by analyzing an extract from vegetation exposed to fall-out from an industrial fire. CDDs/CDFs, chlorinated pyrenes and chlorinated tetracenes could be detected from a Kendrick plot analysis of the ultrahigh resolution mass spectra. Mass accuracies were of the order of 0.5 ppm on standards with external mass calibration and 1 ppm on a sample with internal mass calibration.     

Hybrid polyoxovanadates: anion-influenced formation of nanoscopic cages and supramolecular assemblies of asymmetric clusters

Two novel hybrid polyoxovanadates that are functionalized by (4-aminophenyl)arsonic acid ligands form upon the reduction of vanadates(V) in aqueous systems, whereby the underlying condensation reactions are influenced by the nature of the employed acid. In the presence of Cl(-) ions that derive from hydrochloric acid, a tetradecanuclear cage structure [V(IV)(14)O(16)(OH)(8)-(O(3)AsC(6)H(4)-4-NH(2))(10)](4-), whose cavity contains stabilizing halide ions and water molecules, is obtained. When nitric acid is used, a decanuclear [V(10)O(18)(O(3)AsC(6)H(4)-4-NH(2))(7)(DMF)(2)](5-) cluster can be isolated. The latter organizes into a hexagonal packing arrangement in the solid state.