Experimental data obtained using low energy electron beams are presented which show that films of N2O, of several hundred monolayers (ML), spontaneously acquire a positive potential of as high as 5 V. Films do not possess a dipole double layer but for >40 ML display a constant electric field within the material. This new phenomenon is attributed to dipole alignment. The phenomenon also shows a strong temperature dependence. This is revealed by the differing dependence of the surface potential on the film thickness at different temperatures and by electron transmission spectra which display marked structure at 62 K which is absent at 40 K.

Dissociative electron attachment to gas phase glycine generates a number of fragment ions, among them ions observed at the mass numbers 15, 16 and 26 amu. From stoichiometry they can be assigned to the chemically rather different species NH(-)/CH(3)(-)(15 amu), O(-)/NH(2)(-)(16 amu) and CN(-)/C(2)H(2)(-)(26 amu). Here we use a high resolution double focusing two sector mass spectrometer to separate these isobaric ions. It is thereby possible to unravel the decomposition reactions of the different transient negative ions formed upon resonant electron attachment to neutral glycine in the energy range 0-15 eV. We find that within the isobaric ion pairs, the individual components generally arise from resonances located at substantial different energies. The corresponding unimolecular decompositions involve complex reaction sequences including multiple bond cleavages and substantial rearrangement in the precursor ion. To support the interpretation and assignments we also use (13)C labelling of glycine at the carboxylic group.

Dissociative electron attachment (DEA) to water in the gaseous phase has been studied using two different crossed electron-molecule beam apparatus. Ion yields for the formation of the three fragments H-, O- and OH- were measured as a function of the incident electron energy. The kinetic energies of the fragment ions were measured and compared with the values derived from ab initio calculations to provide information on the energy partitioning in the fragmentation process. Isotope and temperature effects on the attachment process are discussed and the production of OH- via DEA is confirmed.

The formation of O− and O2− following electron impact to O3 in the energy range between 0 and 3eV is revisited using a newly designed trochoidal electron monochromator. The previous observation of a very sharp peak in the O− ion yield at an energy close to zero eV [Phys. Rev. Letters 82 (1999) 5028] is interpreted as an artefact due to multiple reflection of very low energy electrons in the collision chamber of the spectrometer.

The mass spectrum and the appearance energies of the positive ions formed via electron impact ionization of l-alanine have been measured for the first time in a crossed electron-molecule beam experiment with a high-resolution electron beam. The ionization energy of the molecule and the appearance energies of the fragment ions were obtained from ion efficiency curves. Additionally, high-level quantum chemical calculations of the reaction enthalpies for dissociative ionization into positive ions and neutral radicals were performed and the results were compared with the experiment. On the basis of the calculations possible ionic structures for the measured ions were assigned. The value of the ionization energy for the parent ion with m/z=89 was determined experimentally to be 9.12±0.1eV. For the principal positive fragment ions with m/z of 74, 44 and 28 the experimental values of the appearance energies are 10.74±0.1, 9.10±0.05 and 10.85±0.1eV, respectively.

Low-energy electron attachment to SF5Cl was studied at high energy resolution by mass spectrometric detection of the product anions. Two variants of the laser photoelectron attachment (LPA) technique (Kaiserslautern) were used for determining the threshold behaviour of the yield for SF5− formation at about 1meV resolution, and to investigate the relative cross sections for Cl−, FCl−, and SF5− formation towards higher energies (up to 1eV) at about 20meV resolution. Thermal swarm measurements (Birmingham) were used to place the relative LPA cross sections on an absolute scale. A trochoidal electron monochromator (Innsbruck) was used for survey measurements of the relative cross sections for the different product anions over the energy range of 0–14eV with a resolution of 0.30eV. Combined with earlier beam data (taken at Berlin) [M. Fenzlaff, R. Gerhard, E. Illenberger, J. Chem. Phys. 88 (1988) 149], the present experimental results provide a detailed set of partial cross sections for anion formation in low-energy electron collisions with SF5Cl.

A complementary study of the interaction of SF5Cl in the gas phase with vacuum-UV photons and low-energy electrons from the onset of ionisation, ca. 12eV, up to 20eV is presented. The photon-induced experiments have used tunable vacuum-UV radiation from a synchrotron and threshold photoelectron photoion coincidence spectroscopy for product ion detection, the electron-induced experiments a trochoidal electron monochromator and a quadrupole mass spectrometer. The strengths and limitations of both experiments are contrasted, the main difference being the absence of state selectivity in the electron-induced study. The parent cation is not observed in either study, suggesting that its ground electronic state is repulsive following Franck–Condon vertical excitation. The fragment cations SF5+, SF4Cl+, SF4+ and SF3+ have been observed in both studies, with reasonable agreement in their threshold appearance energies. Using a variant of threshold photoelectron photoion coincidence spectroscopy applicable when the ground state of the parent cation is repulsive, the first dissociative ionisation energy of SF5Cl is determined to be 12.3±0.2eV, leading to a value for the adiabatic ionisation energy for the SF5 radical of 9.92±0.28eV. The electron-induced experiment is sensitive to ion-pair production, and onsets for F+ and Cl+ production have been observed which are only possible energetically if the accompanying fragments are the anions SF4Cl− and SF5−, respectively. A lower limit for the electron affinity of the SF4Cl radical of 4.88eV is determined, a value confirmed by ab initio calculations. The electron-induced experiment is very sensitive to gas impurities, and the effects of minute quantities of SF4, FCl, Cl2 and possibly SF2 in the gas sample are observed.

Electron impact ionization of dinitrogen pentoxide for incident electron energies up to about 25eV 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±0.30eV, has not been observed previously. This appearance energy is close to the calculated threshold.

Electron attachment was studied in gaseous dinitrogen pentoxide, N(2)O(5), for incident electron energies between a few meV and 10 eV. No stable parent anion N(2)O(5) (-) was observed but several anionic fragments (NO(3) (-), NO(2) (-), 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 N(2)O(5) fragmentation. Estimates of the cross sections for production of each of the anionic fragments were made and suggest that electron attachment to N(2)O(5) is amongst the most efficient attachment reactions recorded for nonhalogenated polyatomic systems.

The ion extraction efficiency from a trochoidal electron monochromator was investigated for the same set-up as used in previous experiments. Using the Simion program the ion trajectories in the monochromator were simulated and the ratio of the extracted ions to all ions produced was estimated. The extraction efficiency was found to change very dramatically even at low ion energies, thus, deforming measured attachment cross sections. The results of the simulation were then applied to previously measured cross-section data for dissociative electron attachment to ozone. The corrected data showed very good agreement with the experiments of other authors.

We present results of a crossed electron/molecule beams study concerning dissociative electron attachment (DEA) to CHF2Cl. This study was performed in the electron energy range from about 0–10 eV and at a gas temperature of 300 K. Four fragment negative ions (Cl−, F−, CClF− and CF2−) were observed. The following partial absolute cross-sections for DEA to CHF2Cl were obtained, 2×10−19cm2 at the 1.1 eV resonance for Cl−, 3×10−20cm2 at the 3.4 eV resonance for F−, ≈2×10−21 at the 3.0 eV resonance for CClF− and ≈3×10−21 at the 8.6 eV resonance for CF2−. Using the cross-section functions obtained, total rate coefficients for DEA to CHF2Cl were calculated giving a value of 9.0×10−13cm3s−1 at room temperature. Present results are compared with previous data allowing thus to clarify existing discrepancies.

Electron impact ionization of the chlorodifluoromethane molecule is studied using crossed beams of high-resolution electrons and an effusive molecular beam of CHF2Cl. Ionization energies (IEs) for many positive ions from CHF2Cl (CHF2Cl+,CF2Cl+,CHFCl+,CFCl+,CHF2+,CF2+,HCl+,Cl+,CF+,CH+,F+ C+) are determined from a careful examination of the threshold behavior of the ionization cross sections. Reaction pathways for the dissociative ionization products are suggested using known thermodynamic quantities. Surprisingly, it is observed that the ionization threshold for the parent positive ion IE(CHF2Cl+/CHF2Cl)=12.50(±0.05) eV lies above that for the fragment ions CHF2+, CHFCl+, and CF+ [IE(CHF2+/CHF2Cl)=12.24(±0.03) eV, IE(CHFCl+/CHF2Cl)=12.3(±0.05) eV, and IE(CF+/CHF2Cl)=11.5(±0.1) eV]. Experiments using a three sector field BEE mass spectrometer provide evidence for the existence of two states of the parent CHF2Cl+ ion, one exhibiting a short lifetime of about 2 μs and another parent ion state which appears to be stable on the time scale of the experiment (>20 μs) with an IE of 12.50 eV.

The rate constant for dissociative electron attachment to ozone has been derived over the energy range from about 0 to 10 eV using recently measured and also corrected cross section data. The new rate constant data sets for two partial dissociative channels, as well as for the total dissociative electron attachment, are compared with previously reported values, and existing discrepancies are discussed.

We report the results of the experimental determination of the appearance energy values AE(Xn + /X) for the formation of multiply charged Ne, Ar and Xe ions up to n = 4 (Ne), n = 6 (Ar) and n = 8 (Xe) following electron impact on Ne, Ar and Xe atoms using a dedicated high-resolution electron impact ionization mass spectrometer. The data analysis uses the Marquart-Levenberg algorithm, which is an iterative, nonlinear least-squares-fitting routine, in conjunction with either a two-function or a three-function fit based on a power threshold law. This allows us to extract the relevant AEs and corresponding exponents for a Wannier-type power law from the measured near-threshold data. The values of the AEs determined in this work are compared with other available experimental and spectroscopic values of the AEs and the extracted exponents are compared with other available experimental data and with the predictions of the various Wannier-type power law models.

Using a recently constructed high resolution crossed electron/molecular beam apparatus consisting of a hemispherical electron monochromator and a quadrupole mass spectrometer we have measured the relative production cross sections for CI – and F – via electron attachment to CF 2 Cl 2 . The relative Cl – cross section is placed on an absolute scale by reference to an absolute rate coefficient using a calibration method involving integration of the measured anion signal. The most efficient Cl – production process is at about zero energy and its magnitude is resolution limited. The present high resolution value of 6 × 10 −16 cm 2 compares well with an earlier value reported by Chen and Chantry. A second peak is detected at around 0.8 eV in accordance with some of the earlier beam and swarm measurements. The observed production of F – has an appearance energy of 1.9 eV and the energy of maximum cross section is 3.36 eV, the latter value comparing well with several previous studies.