[en] The study of dissociative electron attachment to CCI₃Br molecule has been performed in the electron energy range from 0 to about 2 e V and in the gas temperature range from 293 K to 478 K using a crossed electron-molecular beams apparatus with a temperature regulated, effusive molecular beam source. Strong enhancement of the negative ion production with the gas temperature has been observed for the overall negative ion yield and for CI^-/CCI₃Br reaction channel at low electron energies (approx or approx 0 eV). Activation energies for dissociative electron attachment of (123 + - 20) meV and (65 + - ) meV have been estimated for the overall negative ion formation and for the CI^- reaction channel. The dissociative electron attachment cross section for Br^-/CCl₃Br reaction channel was at low electron energies temperature independent. At the 0.6 eV (Br^-/CCl₃Br) and 0.65 eV (Cl^-/CCl₃Br) resonances the cross-sections were temperature independent. At the elevated gas temperatures above 422 K strong decrease of the negative ion yield has been observed for dissociative electron attachment CCl₃Br assigned to the catalytic thermal decomposition of molecules on the iron surface of the molecular beam source (Authors)

[en] Using a new crossed electron-molecule beam apparatus relative gross sections for dissociative electron attachment to SF₆, CCI₄, CCI₂F₂, CHCI₃ and CHBr₃ molecules have been measured at low electron energies from about 0 to 2 e V. The electron energy resolution measurements of the electron beam and the calibration of the electron energy scale have been performed with SF₆ and CCI₄ as a test and calibrant gases. Using a Trochoidal Electron Monochromator electron energy resolution of the electron beam with Full With at Half Maximum of 17 m eV has been achieved. The present measurements of dissociative electron attachment to first four molecules are in excellent agreement with previous studies. The dissociative electron attachment to CHBr₃, has been measured in a crossed beam experiment for the first time. Two resonances have been observed at about 0 eV and about 0,6 eV. (Authors)

[en] The threshold energy and the threshold behaviour for electron impact ionization of CH₄ were investigated at two temperatures, 293 and 693 K. The study was performed with a crossed electron-molecule beam apparatus with an electron energy resolution of 120 meV full width at half maximum. The values of the ionization energies (IEs) and the threshold behaviour were determined using a fitting procedure involving a convolution of the cross section and the electron energy distribution function. At 293 K the following IEs were obtained: IE(CH₄⁺/CH₄) = 12.65 ± 0.4 eV, IE₁(CH₃⁺/CH₄) = 13.58 ± 0.1 eV (ion pair) and IE₂(CH₃⁺/CH₄) = 14.34 ± 0.1 eV. At 693 K a red shift in these IEs of about 0.14 eV was observed for both CH₄⁺/CH₄ and CH₃⁺/CH₄ processes, which reflects the change in the internal energy of CH₄ with increasing temperature. In addition, at 293 K IEs were determined also for the small fragment ions, i.e. IE(CH₂⁺/CH₄) = 15.1 ± 0.1 eV, IE(CH⁺/CH₄) = 19.8 ± 0.1 eV and IE(C⁺/CH₄) = 20.5 ± 0.2 eV

[en] Electron attachment (EA) reactions play an important role in various fields of chemistry, physics and in a large number of technological applications. Its strong dependency on the electron kinetic energy was shown in previous works. The study of the gas temperature effect on the dissociative electron attachment (DEA) to the chloro-bromo-methanes was undertaken, in particular: chloro-bromo-methane CH₂BrCl, dichloro-bromo-methane CHCl₂Br, chloro-dibromo-methane CHClBr₂, chloro-fluoro-dibromo-methane CFClBr₂ and trichloro-bromo-methane CCl₃Br. The experiment was performed in the electron energy range from 0 to 2 eV and in the gas temperature range from about 300 K to about 500 K using a new crossed electron-molecular beams apparatus with regulated temperature. All these reactions are exothermic with a competition between two separate reaction channels ( Cl^- and Br^- ). The reaction products distribution into these channels as a function of the electron energy and the gas temperature was analysed. Br- was founded as the dominant reaction product corresponding to the DEA reactions of CH₂Br₂Cl, CHCl₂Br, CHClBr₂ and CFClBr₂, while in the case of CCl₃Br, at gas temperatures above 348 k Cl^- was the dominant ion in the whole electron energy range. At gas temperatures above 420 K a strong decrease of both ions signals was observed, this is attributed to thermal decomposition. (nevyjel)

[en] The work investigates the emissions of NO and NO₂, which arise from the combustion of hydrogen in the air. Measurements were performed with both diffuse and premixed flames on single-channel burners of different diameters. The power of the investigated flames ranged from 33 W to 120 W. NO emissions ranged from 0.015 g/kWh to 0.26 g/kWh of heat released. NO₂ emissions did not reach the detection limit of the sensor used. We compared the obtained results with the work of other authors and with current standards for NO_x emissions. (authors)

[en] We have determined appearance energies AE(Xⁿ⁺/X) for the formation of multiply charged He, Ne, Ar, Kr and Xe ions up to charge state n=2 (He), n=4 (Ne), n=6 (Ar), n=6 (Kr) and n=8 (Xe) using a recently commissioned high-resolution electron impact ionization mass spectrometer. The data analysis is based on the Marquart-Levenberg algorithm, involving an iterative, non-linear least-squares fitting of the threshold data assuming a 2-function or a 3-function fit based on a Wannier-type power law. This allows us to extract the relevant AEs and corresponding Wannier exponents

[en] Using the laser photoelectron attachment method with an energy width ≤1 meV at low energies (≤172 meV) and an electron beam method (energy width about 70 meV) at higher energies (up to 2 eV), we have determined absolute cross sections σ_e (E) for dissociative electron attachment to the dipolar molecules CH₂Br₂ and CCl₃Br by normalization to known electron attachment rate coefficients. At thresholds for vibrational excitation of the CH₂Br₂ molecule, the DA cross section exhibits pronounced structure due to coupling of the attachment process with scattering channels; below the ν₃=1 onset for the symmetric CBr₂ stretch vibration, a clear vibrational Feshbach resonance is observed. At low energies the cross sections σ_e (E) show an energy dependence between E^-1/2 and E^-1, in essential agreement with predictions of an extended Vogt-Wannier (EVW) capture model which includes the long-range electron-dipole interaction in addition to the polarization force. The determined absolute values are, however, substantially smaller than those predicted by the EVW model. Semiempirical R-matrix calculations have been carried out which show that at low electron energies (E < 0.15 eV) Br^- formation from CCl₃Br proceeds by s-wave attachment to the anion ground state while a broad peak, observed around 0.6 eV and evolving predominantly into the Cl^- channel, is due to an excited anion state. Comparisons are made with cross sections and rate coefficients obtained in previous photoelectron attachment work (TPSA) and in electron beam as well as swarm experiments. Based on our joint experimental results for σ_e (E), we report the electron temperature dependence of the rate coefficients k_e (T_e) for free electron attachment involving a Maxwellian electron ensemble and a gas at room temperature (T_G=300 K). (author)

No abstract available

[en] Electron guns are devices commonly used to produce ions in mass spectrometry. In order to ionize at atmospheric pressure, we have developed a source of low-energy electrons, which works on the principle of electrons passing from a vacuum through a thin S_i3N₄ membrane into the atmosphere. (authors)

[en] The threshold behaviour of the cross-section for cations formed via electron impact ionization to methane (CH₄, CH₃D and CD₄), ethane (C₂H₆) and propane (C₃H₈) has been studied in a crossed electron/neutral beams apparatus with mass spectroscopic analysis of the ions. The appearance energies of the ions formed via electron impact ionization to these molecules were determined at room and at elevated temperatures (about 700 K). At elevated gas temperatures a decrease of the appearance energies has been observed for all molecules (red shift). The red shift appears to depend on the size and on the isotopic composition of the molecules. These results indicate that at very high gas temperatures the cross-sections for electron impact ionization in the threshold region changes may substantially differ from the low temperature one. Additionally, differences in the appearance energies due to isotopic substitution have been observed for molecules CH₄, CH₃D and CD₄. (author)