Total Cross Sections For Electron Research Articles

Absolute total electron-scattering cross sections of N 2O and OCS in the low-energy region

Absolute total cross sections for electron scattering from the N2O and OCS molecules at low energies have been measured using the linear transmission technique. The results are compared with existing experimental and theoretical data. Quite good agreement was found with the calculations of Lynch et al. for OCS.

Interaction of oxygen with (100) surfaces of Fe-3wt%Si and electron stimulated oxygen desorption

At elevated temperatures the equilibrium segregation of Si on the surface of Fe-3wt%Si single crystals was studied [1]. For a (100) surface at saturation a complete c(2 × 2)Si structure was observed by LEED. The present paper is on the interaction of gaseous oxygen with such surfaces. Different oxygen adsorption and oxidation processes were observed in dependence on the sample temperature. At temperatures below about 400 δ C, oxygen is adsorbed on Fe and Si atoms with a relative high initial sticking probability and both elements are oxidized during further oxygen exposure. At higher temperatures between 400 to 600 ° C a two step oxidation process of only Si was observed, characterized by initial oxygen adsorption on the Si atoms and a subsequent oxidation of the Si-O adsorption complex to SiO 2 species. For temperatures above 550 °C increasing thermal decomposition of the SiO 2 species was observed. For different initial surface compositions the kinetics of oxygen uptake were studied in dependence on sample temperature and oxygen exposure. The kinetics of oxygen adsorption on the Si atoms and the oxidation of the Si atoms are strongly influenced by the primary electron beam used for AES analyses. By electron bombardment the SiO 2 species are decomposed and oxygen desorbs. The total cross section for electron stimulated decomposition of the SiO 2 species appears to be coverage dependent. The total cross section for desorption of adsorbed oxygen from the Si atoms was determined, its dependence on primary electron beam energy, primary beam current and sample temperature was studied.

Total cross sections for electron–lithium scattering

We have calculated electron–lithium total scattering cross sections using the simplified second Born and corrected static approximations. The results of the present calculations have been compared with the estimated values of Walters and available experimental data.

Production of stable and autoionizing O2− and NO− ions in CsO2 and CsNO collisions

Abstract We present absolute total cross sections for electron and ion production in CsNO and CsO 2 collisions. The laboratory energy of the cesium atoms varied between 30 and 3000 eV. The branching ratio between electron and ion production in these systems provides a direct measure for the amount of molecular anions which are produced in stable or autoionizing vibrational states. The absolute magnitude of the observed cross sections shows that the ionization process is due to a curve crossing between the potentials of the covalent and ionic ground states. The experiment shows that CsNO collisions predominantly lead to production of NO − ions in the vibrational ground state. For both CsNO and CsO 2 collisions the distribution over vibrational states of the molecular anions is a function of the collision energy. The experimental results are discussed on the basis of several models.

Total cross section measurements for positron and electron scattering on molecular hydrogen between 8 and 400 eV

An apparatus for the measurement of positron and electron total cross sections on gases is described. The low-energy positrons are produced by moderating high-energy positrons from beta -decay sources. The authors used a11C positron source, produced at a proton accelerator and, alternatively, a22Na source, combined with various moderators. For electron measurements the secondary electrons originating from the moderator are used. The beam transport system consists of electrostatic lenses and a weak magnetic lens located in the middle of the gas cell. The discrimination against forward scattering is characterised by a cut-off angle of about 6 degrees . The authors' e+-H2and e--H2data are compared with the results of recent measurements of similar accuracy performed at University College, London, and Wayne State University (Detroit), and with other e--H2data. The agreement is satisfactory.

E±−COande±−CO2total cross-section measurements

As part of a continuing series of investigations, total scattering cross sections have been measured in the same apparatus for positrons and electrons colliding with CO and C${\mathrm{O}}_{2}$ using a beam-transmission technique. The projectile impact energies are in the range 1-500 eV for ${e}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{-}\mathrm{CO}$, 30-500 eV for ${e}^{+}\ensuremath{-}\mathrm{C}{\mathrm{O}}_{2}$, and 100-500 eV for ${e}^{\ensuremath{-}}\ensuremath{-}\mathrm{C}{\mathrm{O}}_{2}$. An important aspect of our work is to compare the corresponding positron and electron total cross section (${Q}_{T}$) curves for a given target gas. For both CO and C${\mathrm{O}}_{2}$ the electron ${Q}_{T}$ values are generally larger than the positron results. For both gases at low energies there are relatively narrow shape resonances for electron scattering and noticeable increases in ${Q}_{T}$ after the positronium-formation thresholds for positron scattering. At the highest energies investigated there are indications of a tendency toward merging of the positron and electron curves for each gas. A striking similarity is found between the present ${e}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{-}\mathrm{CO} {Q}_{T}$ curves and the ${e}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{-}{\mathrm{N}}_{2} {Q}_{T}$ curves obtained by Hoffman et al. [Phys. Rev. A 25, 1393 (1982)], in that the corresponding shapes and magnitudes are very nearly the same. Estimates of potential experimental errors, as well as the experimental discrimination against projectiles scattered at small forward angles, are made.

Elastic scattering of electrons by hydrogen molecules in the modified Glauber approximation

A modified Glauber approximation has been employed to investigate the elastic scattering of electrons by the hydrogen molecules in the intermediate-energy range (50-1000 eV). The exchange effects are included through the Glauber-Ochkur approximation. In general the effect of multiple scattering is found to be small and the differential cross sections agree very well with the absolute experimental data for $E\ensuremath{\ge}100$ eV. The total cross sections for electron as well as positron scattering are also obtained via the optical theorem. The values are in good agreement with the available experimental data.

Total cross sections for electrons scattered from gases: 0.5-3.0 keV range on Ar

Absolute total cross sections for electron scattering on Ar have been measured over the energy range of 0.5-3.0 keV. The correction due to the small-angle scattering was carried out using the theoretical differential elastic and inelastic cross sections. The corrected total cross sections agree well with the earlier experimental and theoretical results. The comparison with the high-energy Born theory is discussed.

Cross sections for symmetric charge transfer and proton transfer reactions of internal energy selected NH3+ (v)

Absolute total cross sections for electron and proton transfer reactions of NH3 selected in vibrational levels from v = 0 to 10 have been measured by photoion–photoelectron coincidence. The proton transfer reactions were determined at relative translational energies between 0.1 and 1 eV, while the electron transfer reactions were measured between 1 and 100 eV and at 3000 eV. Although the Franck–Condon factors between v = 0 and v = 5 of the NH3 (v = 0)→NH3+ (v) transition change by a factor of 35, the cross sections for charge transfer vary only by a factor of two. By comparing the measured cross sections with the Langevin collision cross sections, we show that the internal energy plays a role only for impact parameters larger than the Langevin orbiting impact parameter. A model which divides the charge transfer reaction into two types, one involving intimate collisions, the other large impact parameter collisions, is introduced. The model is used to derive the charge transfer probability as a function of impact parameter for various combinations of NH3+ vibrational and relative kinetic energies.

Total cross sections for electron scattering from Ne, Ar, Kr and Xe

Total cross sections have been measured for electron scattering on Ne, Ar, Kr and Xe in the impact energy range between 25 and 750 eV. The method used has been introduced by Blaauw et al. (1980) for the same measurement with He and N2 as targets. It is a linearisation of the Ramsauer-type experiment, which enables good angular and energy resolution; the accuracy in the total cross sections obtained is better than 5%. Substantial differences are found with experimental data of other groups, which can often be attributed to shortcomings in their experimental set-up. The best agreement is obtained with the recent data of Kauppila, Stein and co-workers (1980). Above 100 eV our Ne and Ar data can be compared with theoretical calculations, of which the optical model results of Joachain et al. (1979) rapidly converge to the present ones. Good agreement is also found with the semi-empirical total cross sections of de Heer et al. (1979).

Total cross sections for electron scattering by molecular hydrogen

Total cross sections for electron scattering by H2 are obtained for impact energies ranging from 25 to 750 eV. The method used is a linearisation of the Ramsauer-type experiment, which enables good angular and energy resolution; the accuracy obtained in the total cross sections is better than 4%. The authors compare their results with existing experimental data of other groups in this energy range. By means of analysis of theories and experiments on total cross sections for elastic scattering, excitation and ionisation the authors evaluate a set of semi-empirical total cross sections from 20 up to 2000 eV impact energy, which are accurate to about 5% over most of this energy interval. In the overlapping range the authors find excellent agreement of the data obtained thus with our experimental results.

Total cross sections for electron scattering from N2and He

Total cross sections for electron scattering from N₂and He

Total cross sections for electron scattering by Ne, Ar, Kr and Xe

A set of total cross sections for scattering of electrons by Ne, Ar, Kr and Xe has been evaluated over the energy range of about 20 to 3000 eV by means of the analysis of experiments and theories on total cross sections for elastic scattering, ionisation and excitation, and on differential cross sections for elastic and inelastic scattering. The total cross sections for scattering of electrons are evaluated by adding those for ionisation, excitation and elastic scattering and they are accurate to about 5-10%. They appear to be in very good agreement with the recent experimental results on total electron scattering of Wagenaar et al. (1978).

Absolute total electron scattering cross section of CO, CO 2 and OCS in the low energy region

Absolute total cross sections for electron scattering from CO, CO 2 and OCS molecules at low energies have been measured. An increase of the cross sections due to the formation of negative ion resonance states was observed.

Electron-helium absolute total scattering cross sections from 0.5 to 50 eV

Absolute total cross sections for electron scattering from He have been measured over the energy range from 1 to 50 eV with an accuracy of 3% or better. A novel method employing time-of-flight monochromatization and energy determination of electrons from a pulsed secondary-emission source in transmission through a gas cell has been used. This method is contrasted with conventional ones and a comprehensive error discussion is given. The reported results are then compared to existing experimental and theoretical results. Discrepancies in existing experimental data are resolved and good agreement is obtained with some recent theoretical results.

Total cross sections for electron scattering by He

A set of total cross sections for scattering of electrons by He has been evaluated over the energy range of zero to 3000 eV by means of the analysis of experiments and theories on total cross sections for elastic scattering, ionisation and excitation, and on differential cross sections for elastic and inelastic scattering. Between 0 and 19.8 eV, where no inelastic processes occur, the total cross sections for scattering are equal to those for elastic scattering. Above 19.8 eV the authors have evaluated total cross sections for scattering of electrons by adding those for ionisation, excitation and elastic scattering. The total cross sections thus obtained are probably accurate to about 5% over a large part of the energy range. They appear to be in good agreement with the experimental results of Blaauw et al. (1977).

Transmission experiment for measuring total positron–atom collision cross sections in a curved, axial magnetic field

We describe and analyze a transmission experiment developed for measuring total scattering cross sections for low-energy poistrons (0.3–250 eV) colliding with gases in a region containing a curved, axial magnetic field. It is determined that spiralling does not appreciably increase the beam path length through the curved, axial magnetic field in the gas scattering region. An overall test of the experimental apparatus and technique is made by measuring total cross sections for electrons colliding with helium and argon atoms in the energy range from 1.5 to 30 eV, where it is found that the present measurements are within 15% of the most reliable prior measurements.

Total cross sections for electron scattering from N2and He

An apparatus has been constructed to measure the total cross section for electron scattering by atoms and molecules. It can be viewed as a linearisation of the Ramsauer technique with a well defined solid angle for the analyser/collector. Measurements of He and N2 have been carried out for 15-750 eV electrons. The data obtained link up with the existing data at low energies within the experimental uncertainty. For He perfect agreement is found with the Born approximation above 200 eV.

A study of the negative ion states of selected cyclodienes by electron transmission spectroscopy

Electron transmission spectroscopy is employed to locate sharp variations in the total cross sections for electrons scattered from several cyclic compounds containing two carboncarbon bonds. For each molecule, structure is observed which we associate with the temporary occupation of the two low-lying, normally unfilled, π * orbitals by impacting electrons. Electron affinities are reported for 1,5-cyclooctadiene, 1,4-and1,3-cyclohexadiene, norbornadiene and also cyclohexene, propene, and cis-butene.

Electron scattering by rubidium below the excitation threshold

Total cross sections for electron scattering by rubidium are calculated. The dependence of the ratio of spin-exchange to full differential cross section on the scattering angle is also obtained.