Elżbieta Ptasińska-Denga

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.

Electron collisions with trifluorides: BF3 and PF3 molecules

Absolute total cross sections (TCSs) for electron scattering from boron trifluoride (BF(3)) and phosphorus trifluoride (PF(3)) molecules have been measured using a linear transmission method. The electron energy ranges from 0.6 to 370 eV for BF(3) and from 0.5 to 370 eV for PF(3). The TCS energy dependence for BF(3) exhibits two very pronounced enhancements: resonantlike narrow feature located near 3.6 eV with the maximum value of 19.2 x 10(-20) m(2), and intermediate energy very broad enhancement with two humps, one centered around 21 eV (18.8 x 10(-20) m(2) in the maximum) and the other near 45 eV (19.5 x 10(-20) m(2)). For PF(3) the TCS has quite different low-energy dependence: at 0.5 eV it has a high value of 70 x 10(-20) m(2) and decreases steeply towards higher energies. Beyond the minimum near 5.5 eV, the TCS reveals two distinct humps: the resonant one centered near 11 eV with the peak value of 32.9 x 10(-20) m(2) and the second one much broader around 35 eV (27.9 x 10(-20) m(2)). The present TCSs for trifluorides are compared to each other as well as to previous TCS data for selected perfluorides and to results for their perhydrided counterparts. The differences and similarities in the shape and magnitude of TCSs are pointed out.

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 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.

Electron scattering by trimethylene oxide, c-(CH2)3O, molecules.

Electron-scattering cross sections have been determined for trimethylene oxide, cyclic (CH(2))(3)O molecule, both experimentally and theoretically. The absolute total cross section (TCS) has been measured over energies from 1 to 400 eV using a linear electron-transmission method. The obtained TCS generally decreases with rising energy, except for the 3-10 eV range, where some resonantlike structures are discernible. Integral elastic cross section (ECS) and ionization cross section (ICS) have been also calculated up to 3 keV in the additivity rule approximation and the binary-encounter-Bethe approach, respectively. Their sum, ECS+ICS, is in a good agreement with the measured TCS. Comparison of the TCS energy dependence for trimethylene oxide with that for its isomeric open-chain counterpart--acetone, (CH(3))(2)CO, has also been made. Moreover, examination of experimental TCSs for the cyclic (CH(2))(n)O, n=2-4, ether series reveals that the intermediate-energy molecular TCSs for members of that family can be nicely represented as a sum of the effective TCSs for particular constituents of the molecule, i.e., methylene groups and oxygen atom. Finally, based on these partial TCSs, the TCS for the c-(CH(2))(5)O--the next member of the series--has been determined and compared with the respective ECS+ICS values computed here for this compound.

Collisions of electrons with trimethylphosphine [P(CH3)3] molecules

We report on the absolute total electron-trimethylphosphine scattering cross section (TCS) measured from 0.4 to 400 eV using a linear electron-beam attenuation method. The experimental TCS energy function exhibits very pronounced asymmetric enhancement peaked near 5.5 eV. Calculations were also carried out to obtain the integral elastic and ionization cross sections at intermediate and high energies using the independent atom and the binary-encounter-Bethe approximations, respectively. Their sum, the computed total cross section, is for intermediate energies in a reasonable agreement with the present experimental TCS data. Furthermore, the measured TCS for P(CH{sub 3}){sub 3} is compared with the TCSs for some other phosphines [PH{sub 3}, PF{sub 3}] and other methides [B(CD{sub 3}){sub 3}, N(CH{sub 3}){sub 3}]. Analysis clearly shows that exterior atoms of a molecule influence the scattering process more significantly than the central atom.

Electron collision with sulfuryl chloride (SO2Cl2) molecule

Absolute total cross section (TCS) for electron scattering from sulfuryl chloride (SO2Cl2) molecules was measured in a linear transmission experiment at energies ranging from 0.5 to 150 eV. The most distinct features found in the TCS are the deep minimum located near 1.8 eV and the broad enhancement peaked around 9.5 eV with a shoulder spanned between 3 and 5 eV. At intermediate energies, the present experimental TCS results agree well with our total cross-section estimations, based on calculations of elastic and ionization cross sections. In addition, the calculated total cross section for SO2F2 is reported. The results for e−–SO2Cl2 collisions are compared, for the energy dependence and magnitude, with experimental and computed cross sections for other molecules (SO2F2, SO2ClF) comprising a sulfone group.

Fluorination effects in electron-scattering processes—comparative study

Abstract Systematic studies of electron interaction with perfluorinated targets carried out recently in our laboratory revealed a distinct increase of the total cross section, Q tot , over the impact energy range from a dozen or so to several tens of electronvolts. A likely reason for this striking feature is a significant contribution of elastic processes in this energy range. The ratio of the total ionization electron-scattering cross section to the total cross section can be expressed with a simple regression formula. That formula was used to estimate the GeH 4 ionization cross section.

Scattering of electrons from 1-butene, H2C=CHCH2CH3, and 2-methylpropene, H2C=C(CH3)2, molecules

We report absolute grand total cross sections (TCSs) for electron scattering from 1-butene (H2C=CHCH2CH3) and 2-methylpropene (H2C=C(CH3)2) molecules, measured at electron impact energies ranging from 1 to 400 eV and from 1 to 350 eV, respectively, using a linear electron-transmission technique. The general shape of cross sections for both butene isomers looks similar. Two structures in each TCS energy curve are discernible: a small peak in the vicinity of 2.3 eV and a pronounced very broad enhancement with the maximum located around 8 eV. The magnitude of TCS for 2-methylpropene appears somewhat higher than that for 1-butene below 20 eV, while above 70 eV the TCS curves practically overlap. In addition, comparison is made of TCSs for an ethylene (H2C=CH2) molecule and its mono and double methyl-substituted derivatives: propene (H2C=CHCH3) and 2-methylpropene. (Some figures may appear in colour only in the online journal)

Electron-scattering cross sections for 1-pentene, H2C=CH–(CH2)2CH3, molecules

Cross sections, both experimental and theoretical, are reported for electron scattering from 1-pentene (C5H10) molecules. Absolute grand-total cross sections (TCSs) were measured at electron impact energies ranging from 1 to 300 eV, using a linear electron-transmission technique. The dominant behaviour of the experimental TCS energy function is a distinct asymmetric enhancement with the maximum located around 6.5 eV. Discernible are also three weak TCS structures: a small peak in the vicinity of 1.8 eV and two broad shoulders located between 10 and 30 eV. The additivity rule was employed to calculate the elastic cross section (ECS) from 20 to 3000 eV, while the binary-encounter-Bethe approach was used for the computation of the ionization cross section (ICS), from the threshold up to 3000 eV. Within 30 and 300 eV, the sum of computed cross sections (ECS+ICS) quite reasonably reproduces the experimental TCS values. Comparison is also made between the experimental TCS energy curve for 1-pentene (H2C=CH–(CH2)2CH3) and those measured for the ethylene (H2C=CH2) molecule and its substituted derivatives: propene (H2C=CH–CH3) and 1-butene (H2C=CH–CH2CH3). (Some figures may appear in colour only in the online journal)