Paweł Możejko

Total dissociative electron attachment cross sections of selected amino acids.

Total dissociative electron attachment cross sections are presented for the amino acids, glycine, alanine, proline, phenylalanine, and tryptophan, at energies below the first ionization energy. Cross section magnitudes were determined by observation of positive ion production and normalization to ionization cross sections calculated using the binary-encounter-Bethe method. The prominent 1.2 eV feature in the cross sections of the amino acids and the closely related HCOOH molecule is widely attributed to the attachment into the -COOH pi* orbital. The authors discuss evidence that direct attachment to the lowest sigma* orbital may instead be responsible. A close correlation between the energies of the core-excited anion states of glycine, alanine, and proline and the ionization energies of the neutral molecules is found. A prominent feature in the total dissociative electron attachment cross section of these compounds is absent in previous studies using mass analysis, suggesting that the missing fragment is energetic H-.

Elastic cross-section calculations for electron collisions with XY4 (X=Si, Ge; Y=H, F, Cl, Br, I) molecules

Abstract We report calculations of integral cross-section and differential cross-section for intermediate- and high-energy (20–2000 eV) elastic electron collisions with tetrahedral compounds of silicon and germanium: SiH4, SiF4, SiCl4, SiBr4, SiI4, GeH4, GeF4, GeCl4, GeBr4 and GeI4. The calculations have been carried out using an independent atom model with static-polarization model potential. The present results are compared with available experimental and theoretical data. For collision energies higher than 100 eV, results of present theoretical calculations are in satisfactory agreement with experimental data.

Electron scattering from hexafluoride molecules: WF6 and C2F6. Absolute total cross section measurements from 1 to 250 eV

Electron-scattering absolute total cross sections for tungsten hexafluoride (WF6) and hexafluorethane (C2F6) molecules have been measured in a linear transmission electron-beam experiment within the impact energy range from about 1 to 250 eV. For electron scattering from WF6 the cross section shows a prominent resonant-like peak centred at 3 eV and a very broad enhancement in the energy range between 20 and 70 eV overlaid with some much less pronounced features. The cross section for C2F6 has two resonant structures at 5 and 9 eV, respectively, and a very broad hump ranging from 20 to 60 eV with a distinct shoulder near 20 eV. Comparison of the e--C2F6 total cross section with available low-energy data from other experiments is made. The effect of fluorination is indicated.

Experimental absolute total cross sections for low-energy electron collisions with tetrahedral compounds of germanium:

Absolute total cross section (TCS) of the electron collision with molecules has been measured in a linear transmission experiment for impact energies from 0.5 to 250 eV. The TCS function is dominated by a steep rise towards low energies below 3 eV. At energies above the minimum at 3 eV the TCS shows another enhancement spanned up to about 70 eV on which some resonant-like features are visible: the maximum centred near 6.5 eV and two weak peaks at 16 and 25 eV, respectively. A comparison with the recent measurements taken in the same laboratory for and and for other targets of the same symmetry is made to search for similarities and/or differences between electron scattering TCSs for tetrahedral molecules. The data demonstrate that the general shape of the low-energy TCS for tetrahedral molecules depends on external rather than on central atoms.

Low- and intermediate-energy total electron scattering cross sections for and molecules

Absolute total cross sections for electron collision with and molecules have been measured in a linear attenuation experiment for impact energies ranging from 0.6 to 250 eV. Good agreement of the present results with other experimental data has been found in respect of the energy dependence of the total cross section (TCS). Discrepancies in magnitude are only apparent for the lowest and the highest impact energies applied. Comparison is also made with theoretical calculations. The electron-scattering TCS for shows two distinct resonant maxima: one at 1.7 eV, occurring over a narrow energy range, the other - much broader - near 9 eV. No TCS data for are available for comparison.

Spectrometer for the study of electron-assisted processes

Abstract Equipment built in our laboratory, for the study of the phenomena related to the electron-scattering processes, is described. The apparatus consists of an electron-scattering spectrometer, target flow system and systems for detecting and handling the electronic and/or ionic signal. As examples of the spectrometer application, the presented results are the electron energy-loss spectrum for N 2 , differential cross section for vibrationally inelastic electron scattering from OCS, vibrational excitation function of N 2 and total cross section for electron scattering from NO.

Intrinsic and extrinsic factors in anion electron-stimulated desorption: D− from deuterated hydrocarbons condensed on Kr and water ice films

The results of D(-) ion desorption induced by 3-20 eV electrons incident on condensed CD(4), C(2)D(6), C(3)D(8), C(2)D(4), and C(2)D(2) are presented. These compounds were deposited in submonolayer amounts on the surfaces of multilayer solid films of Kr and nonporous and porous amorphous ice. While desorption of the D(-) anions proceeds via well-known processes, i.e., dissociative electron attachment (DEA) and dipolar dissociation, significant perturbations of these processes due to presence of the different film substrates are observed. We have shown that it is possible to distinguish between the character and nature of these perturbations. The presence of the nonporous ice perturbs the D(-) desorption intensity by affecting the intrinsic properties of the intermediate anion states through which dissociation proceeds. On the other hand, the presence of the porous ice introduces extrinsic effects, which can affect electron energy losses prior to their interaction with the hydrocarbon molecule and/or the energies and intensities of the fragment species after dissociation. Simple mechanisms responsible for the observed variations in the intensities of desorbed anionic signals are proposed and discussed. Electron transfer from transient anion states to electron states of the substrate film or nearby hydrocarbon molecules appear as the most efficient mechanism to reduce the magnitude of the DEA process.

Electron collisions with ethylene oxide molecules

The absolute total cross section (TCS) for electron–ethylene oxide (c-C2H4O) collisions was measured at electron-impact energies extending from 0.7 to 400 eV using the linear electron-transmission technique. In the present TCS energy function a distinct peak is visible near 4.6 eV which may be attributed to formation of a short-lived negative ion. Moreover, at intermediate and high energies the integral elastic (ECS) and ionization (ICS) cross sections were determined numerically. The calculated sum, ECS + ICS, is in good agreement with the experimental TCS in the overlapping energy range. Finally, the present experimental TCS for electron scattering from c-C2H4O is compared with that for its cyclic isoelectronic counterpart c-C3H6, and similarities and differences are pointed out and discussed.

Electron collisions with germane molecules. Absolute total cross section measurements from 0.75 to 250 eV

Absolute total cross section for electron collisions with molecules has been measured in a linear electron transmission experiment for impact energies between 0.75 eV and 250 eV. Experimental cross section function versus energy reveals a resonant-like broad enhancement with maximum between 3 and 4 eV, monotonically decreasing at higher energies.

Electron scattering by sulfur tetrafluoride (SF4) molecules

Absolute total cross section (TCS) for electron scattering from sulfur tetrafluoride (SF4) molecules was measured in a linear transmission experiment at energies ranging from low (0.1 eV) to intermediate (370 eV). Below 1.6 eV the TCS function increases steeply towards lower energies and shows small resonant-like maximum near 0.4 eV. Two other distinct enhancements are located at higher energies: a narrow one is peaked at 12 eV, and a very broad hump is centred near 40 eV. Our experimental TCS results are compared with the previous TCS measurements at low impact energies and at intermediate energies—with our total cross section estimations based on calculations of elastic and ionization cross sections. The TCS for SF4 is also compared with SFn (n = 1, 2, 6) total cross sections.