Total Cross Sections For Electron Research Articles

Positron and electron scattering from alkane molecules

Total cross-sections (TCSs) for 0.2–1000 eV positrons and 0.4–1000 eV electrons colliding with normal-octane and cyclo-octane molecules have been studied using a relative measurement method. The TCS curves for positron and electron vary smoothly and compare well with other alkane molecules, in order of increasing carbon number. For positron scattering, weak humps at 1.5–2.5 eV for both normal- and cyclo-octane were observed. In the energy range lower than 2.2 eV, positron TCSs are roughly equal to or larger than electron TCSs. For electron scattering, a resonance peak at 8 eV and a shoulder at 25.0 eV were observed for both molecules. Over all the energy range, the TCS values for normal-octane are larger than those of cyclo-octane. The positron and electron TCS data for normal- and cyclo-octane molecules are briefly compared with those for normal- and cyclo-hexane.

Total cross sections for electrons scattering from simple molecules containing the larger atom sulfur at 30–5000eV

A complex optical model potential modified by the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds, is employed to calculate the total cross sections for electrons scattering from simple molecules (SO2, H2S, OCS, CS2 and SO3) containing the larger atom, sulfur, at 30–5000eV by using the additivity rule model at Hartree–Fock level. The quantitative molecular total cross section results are compared with those obtained in experiments and other calculations wherever available and good agreement is obtained. It is shown that the additivity rule model together with the complex optical model potential modified by the concept of bonded atom can give the results closer to the experiments than the one unmodified by it. So, the introduction of bonded-atom concept in complex optical model potential betters the accuracy of the total cross section calculations of electrons from the molecules containing the larger atom, sulfur.

An Empirical Formula Approach to Total Cross Sections forElectron Scattering on Polyatomic Molecules

Considering the real experimental process of e-molecule scattering anew empirical formula has been developed to calculate the total crosssections (TCSs) for electron scattering on polyatomic molecules(CH4, C2H2, CH3OH and CH3F). Thepresent results are compared with other available theoretical resultsand experimental data. The new formula incorporates an energyfactor f(E) to represent the elastic and inelasticchanging process during experiments. It depends on no adjustableparameters and has also extended the validity of the empiricalapproaches to lower energy range further.

Total cross-section measurements for positrons and electrons colliding with alkane molecules: Normal hexane and cyclohexane

Total cross sections (TCSs) for $0.2--1000\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ positrons and $0.4--1000\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ electrons colliding with normal hexane and cyclohexane molecules are reported. For positron scattering, low-lying peaks at $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for normal hexane and $1.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for cyclohexane are observed. For both molecules, positron TCSs are larger than electron TCSs below $2.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$; for electron scattering, the main resonance peak in the TCS curve is at $7.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, followed by a shoulder at about $22\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. TCSs for normal hexane are larger than those for cyclohexane for both positrons and electrons over all the energy range. Striking similarities, more pronounced for electron impact, have been observed between $c$-hexane and benzene TCSs and are attributed to the similarity in molecular structure between these two molecules, whereby each has a hexagonal ring based on the six C atoms.

Electron and positron scattering from perfluorocyclobutane(c−C4F8)molecules

Total cross sections (TCSs) are experimentally investigated for 0.8--600-eV electron and 0.7--600-eV positron scattering from $c\text{\ensuremath{-}}{\mathrm{C}}_{4}{\mathrm{F}}_{8}$ molecules using a linear transmission time-of-flight method, and a comparative study of the results is carried out in this paper. Electron-scattering differential cross sections (DCS) measurements carried out for energies 1.5--100 eV are used for a combined TCS and DCS discussion. These DCS results help to offer a better understanding of some of the structures observed in the TCSs. Fingerprints of a low-energy resonance, consistent with large electron attachment cross sections near 0 eV, have been observed below 2 eV where TCSs show a continually rising trend. Another resonance peak at $\ensuremath{\sim}8.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, attributed to dissociative electron attachment with the production of fragmented ions, and a broader one at 16--40 eV, have also been observed. Except for the pronounced shoulder at $\ensuremath{\sim}40\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, there is good qualitative agreement between the TCS result and the integrated cross-section results. Although electron TCSs are found to be generally larger than positron TCSs in the 3--120-eV ranges, these two TCSs, however, show a tendency towards merging above 120 eV.

A Correlation Potential Method for Electron Scattering Total CrossSection Calculations on Several Diatomic and Polyatomic Molecules over Energy Range 10∼5000 eV

A complex optical model potential correlated by the concept of bonded atom, which considers the overlapping effect of electron clouds between two atoms in a molecule, is firstly employed to calculate the total cross sections for electron scattering on several molecules (NH3, H2O, CH4, CO, N2, O2, andC2H4) over the energy range 10∼5000 eV using the additivity rule model at Hartree–Fock level. The difference between the bonded atom and the free one in states is that the overlapping effect of electron clouds of bonded atoms in a molecule is considered. The quantitative total cross sections are compared with the experimental data and with the other calculations wherever available and good agreement is obtained over the energyrange 10∼5000 eV. It is shown that the correlated calculations are much closer to the available experimental data than the uncorrelated ones at lower energies, especially below 500 eV. Therefore, considering the overlapping effect of electron clouds in the complex optical model potential could be helpful for the better accuracy of the total cross section calculations of electron scattering from molecules.

A modification potential method for electron scattering total cross section calculations on several molecules at 30–5000eV

A complex optical model potential modified by incorporating the concept of bonded atom which takes into consideration the overlapping effect of electron clouds between two atoms in a molecule is employed to calculate the total cross sections for electron scattering in such molecules as N2, NO, NO2, CH4, CF4, CF3H, C2H2 and C2H4 at 30–5000eV using the additivity rule model at Hartree–Fock level. The quantitative total cross sections are compared with those obtained in experiments and other theories, wherever available and good agreement is obtained at 30–5000eV. It is shown that the modified calculation results are much closer to the available experimental data than the unmodified ones at lower energies, especially below 500eV. Therefore, considering the overlapping effect of electron clouds in the complex optical model potential could be helpful for better calculation results about electron scattering total cross sections from molecules.

Electron impact ionisation cross-sections of 2-heptanone

The electron impact ionisation of 2-heptanone between 13 and 78 eV is studied using mass spectrometry. CH 3C(O)CH 2CH 2CH 2CH 2CH 3 + and fragment ions are produced with a total cross-section of 5 × 10 −16 cm 2 towards 50 eV. Two ions, identified as CH 3CO + (43 amu) and CH 3C(OH)CH 2 + (58 amu), contribute to about 60% of the total cross-section for electron energies above the ionisation threshold. The detected ions are identified using ab initio calculations. For E = 14 eV, the ion of 58 amu is the most abundant followed by an ion of 59 amu identified as being CH 3C(OH)CH 3 +; they result from a bond cleavage with one or two H atom rearrangements. For E ≥ 48 eV, the ion of 43 amu is the most abundant; it results from an α-cleavage reaction in the molecular ion.

Elastic and total cross-sections for electron scattering by acetylene in the intermediate energy range

We present a joint theoretical-experimental study on electron scattering by C2H2 in the intermediate energy range. We report calculated elastic differential, integral, and momentum-transfer as well as total (elastic + inelastic) and absorption cross-sections at impact energies ranging from 10 to 500 eV. Also, experimental absolute elastic cross-sections are reported in the (50-500)-eV energy range. A complex optical potential is used to represent the electron-molecule interaction dynamics. The iterative Schwinger variational method, combined with the distorted-wave approximation, is used to solve the scattering equations. Experimentally, the angular distributions of the scattered electrons are converted to absolute cross-sections using the relative flow technique. The comparison of our calculated with our measured results, as well as with other experimental and theoretical data available in the literature, is encouraging.

Total Cross Sections for Electron Scattering from CF4, CF3H, CF2H2, and CFH3 Molecules in Energy Range from 100 to 3000 eV**The project supported by National Natural Science Foundation of China under Grant No. 10174019

The additivity rule has been employed to calculate the total cross sections for electron scattering by CF4, CF3H, CF2H2, and CFH3 molecules over an incident energy range from 100 to 3000 eV. Compared with other calculations and experimental data for CF4, excellent agreement has been obtained. Above 1000 eV, there are no experimental data for CF3H, CF2H2, and CFH3, so the present results can provide comparison and prediction for experimental research.

Total cross sections for electron and positron scattering from 4-fluorobenzaldehyde (C6H4(CHO)F) molecules

Total cross sections for electron and positron scattering from 4-fluorobenzaldehyde (C6H4(CHO)F) molecules

Total cross sections for scattering of electrons from O 2 , H 2 O, H 2 , O 3 , CO and CO 2 at 100–2000eV

A complex optical model potential rewritten by the concept of bonded atom, which considers the overlap of electron clouds, is employed to calculate the total cross sections for electron scattering from several simple molecules (O2, H2O, H2, O3, CO and CO2) consisting of C, H and O atoms in an incident energy range of 100–2000eV by the use of the additivity rule at Hartree–Fock level. In the study, the complex optical potential composed of static, exchange, correlation polarization plus absorption contributions firstly uses the bonded-atom concept. The quantitative molecular total cross section results are compared with experimental data and with the other calculations wherever available and good agreement is obtained. It is shown that the additivity rule along with the complex optical model potential rewritten by the concept of bonded atom can be used successfully to calculate the total cross section of electron–molecule scattering above 100eV, whereas the rule together with the complex optical model potential not rewritten by the concept of bonded atom is only successfully used above 300–500eV. So, the introduction of the bonded-atom concept in the complex optical potential can improve the accuracy of the total cross section calculations.

Experimental investigation of electron and positron interactions with monosubstituted and disubstituted benzene derivatives: fluorobenzene, 1, 3-difluorobenzene and 1, 4-difluorobenzene molecules

Electron and positron scattering from fluorobenzene (C6H5F), 1, 3-difluorobenzene (1, 3-C6H4F2) and 1, 4-difluorobenzene (1, 4-C6H4F2) molecules have been investigated experimentally using the linear transmission time-of-flight method. Total cross sections (TCSs) were measured and determined for 0.8–600 eV and 0.7–600 eV, respectively, for electron and positron scattering from 1, 3-C6H4F2 and 1, 4-C6H4F2 molecules, and 0.4–1000 eV and 0.2–1000 eV, respectively, for electron and positron scattering from C6H5F molecules. A broad resonance structure has been observed in the C6H5F electron TCSs at 0.8–1.6 eV, corresponding to the 1.6 eV 2E2u C6H6 resonance structure. This broad structure seems to be made of two structures at 0.8 eV and 1.4 eV, which should mean that the original single 1.6 eV resonance peak in the C6H6 parent molecule has split into two upon the monosubstitution of its H atom by the F atom. 1, 3-C6H4F2 electron TCSs show a rising trend below 2 eV, a feature attributed to the polar nature of these molecules. Above 4 eV for all these three molecules, electron TCSs are greater than positron TCSs by a factor of ∼2 at energies up to 40 eV.

Total cross sections for electron and positron scattering from 4-fluorobenzaldehyde (C6H4(CHO)F) molecules

A linear transmission time-of-flight method has been used to measure total cross sections (TCSs) for 0.4–1000 eV electron and 0.2–150 eV positron scattering from 4-fluorobenzaldehyde (C6H4(CHO)F) molecules. The disubstitution of the C6H6 parent molecule's two H atoms by the CHO radical and F atom in the 1- and 4-positions, on the benzene ring, has resulted in an electron TCS curve that shows that the original benzene ring symmetry has been partially preserved; a 1.6 eV peak corresponding to the 1.6 eV 2E2u C6H6 resonance peak, a 2.8 eV weak peak in contrast to a minimum for C6H6, a 4.6 eV shoulder corresponding to the 4.93 eV 2B2g resonance peak for C6H6, the main resonance peak centered at 8 eV corresponding to the 9.5 eV 2E1u main resonance peak for C6H6, and the characteristic change of the TCS slope producing a weak shoulder centered at 50 eV for both molecules. On the contrary the positron TCSs show low energy features that differ greatly from the parent C6H6 molecule; two relatively sharp peaks centered at 1 and 4 eV in contrast to the almost smooth and structureless 0.7–10 eV C6H6 peak. Nevertheless, these two positron TCSs resemble each other below 1 eV and above 6 eV.

Contrasting low-energy behaviour in total cross sections for electron and positron scattering from benzene molecules

Marked differences of a rise and a drop in total cross sections below 1 eV between electron and positron impacts, respectively, are experimentally observed for benzene. The present result for electron scattering becomes flat below 1 eV, and smoothly connects with that of Gulley et al (1998 J. Phys. B 31 2735), which shows a sharp rise below 500 meV. The present result for positron reaches a peak at around 1.5 eV and drops relatively sharply below this energy. These remarkably opposite characteristics, i.e., a sharp rise or drop with respect to decreasing incident energy, are attributable to the delicate balance between the attractive and repulsive interactions which results in a virtual state for electron impact, hence causing the sharp increase while the near-zero scattering for positron impact causes the sharp drop.

Total Cross Sections for Electron Scattering from the Isoelectronic(Z = 14) Molecules (C2H2, CO, HCN and N2) at100–5000 eV

A complex optical model potential correlated by the concept of bondedatom, which considers the overlapping effect of electron clouds betweenthe two atoms in a molecule, is employed to calculate the total crosssections for electron scattering from the isoelectronic (Z = 14)molecules (C2H2, CO, HCN, andN2) at 100–5000 eV using the additivity rule at the Hartree–Focklevel. The difference between the bonded atom and the free one is thatthe overlapping effect of electron clouds of bonded atoms in moleculesis considered. The quantitative molecular total cross section resultsare compared with the experimental data and with other calculations available and good agreement is obtained above 100 eV. It isshown that the additivity rule along with the complex optical modelpotential considering the overlapping effect of electron clouds cangive results better than when uncorrelated by it. The correlatingcalculations are much closer to the experiments than thespherical-complex-optical-potential results in the lower energy region[Phys. Rev. A 45 (1992) 202]. Therefore, considering the overlappingeffect of electron clouds in the complex optical potential could behelpful for the better accuracy of the total cross section calculationsof electron scattering from molecules.

A comparative study of electron and positron scattering from chlorobenzene (C6H5Cl) and chloropentafluorobenzene (C6F5Cl) molecules

Total cross sections (TCSs) for electron and positron scattering from chlorobezene (C6H5Cl) and chloropentafluorobenzene (C6F5Cl) molecules have been measured by using the linear transmission time-of-flight method. The impact energies are from 0.4 eV to 1000 eV and 0.2 to 1000 eV for positron and electron impacts, respectively, for scattering from C6H5Cl molecules, and 0.8 eV to 600 eV for electron and 0.4 to 600 eV for positron scattering from C6F5Cl molecules. Two resonance structures are observed in the C6H5Cl electron TCSs at 0.8 eV and 2.5 eV, which merge to the single resonance at 1.6 eV of the C6H6 molecule. This is an evidence of the splitting of the degenerate e2u orbital of the C6H6 molecule into two upon substitution of an H atom by the Cl atom. C6F5Cl electron TCSs are lower than the positron TCSs at 2–4 eV, otherwise elsewhere, electron TCSs for both C6H5Cl and C6F5Cl are greater than positron TCSs by a factor of 1–2 at energies up to 30 eV. In the comparative studies of TCSs for C6H5Cl with C6H6 and C6F5Cl and C6F6, the magnitude of TCSs is found to be in the order of the molecular size over all energy ranges, except positron TCSs for C6H5Cl and C6H6 below 600 eV.

Isomer effects on the total cross section for electron scattering fromC4F6 molecules

The absolute total cross section (TCS) for electron scattering from hexafluoro-1,3-butadiene(1,3-C4F6) was obtained in a transmission experiment for electron impact energies from0.6 to 370 eV. The TCS energy function has two pronounced enhancementsseparated by a deep minimum located near 2.6 eV: a low-energy hump around1 eV and a dominant very broad enhancement centred near 30 eV. The1,3-C4F6 TCS results are compared with the data for hexafluoro-2-butyne(2-C4F6) and the influence of the structural differences on the electron-scattering TCS for isomers of theC4F6 molecule (isomeric effect) is explicitly indicated. The most pronounced role of the moleculargeometry on the magnitude and shape of the TCS energy dependence is observed atthe lowest energies studied. Above 40 eV the TCSs for both isomers are closeto each other. Some conformities of TCSs within a series of perfluorocarbons(C2F4,1,3-C4F6, C6F6) as well as in a series of their hydrocarbon counterparts(C2H4,1,3-C4H6, C6H6) are also pointed out and discussed.

Elastic scattering of low-energy electrons by cadmium atoms

Experimental results on the differential cross sections of 180° elastic electron scattering and the total cross section of electron scattering by cadmium atoms in the energy range 0–6 eV are reported for the first time. Distinct shape resonances with the (5s 25p)2 P 0 and 5s5p 2 configurations are revealed in the near-threshold range and at E≈4 eV. In the range 3.0–3.7 eV, the differential cross section exhibits extra singularities that are probably related to the d-wave shape resonance. The resonance contribution to the backscattering cross section near 4 eV is found to be about 20%.

Total cross sections for electron scattering on polyatomic molecules—considering two different shielding effects

Considering the not fully transparency of the molecule by electron and the overlapping between the atoms in the molecule, a new modified formulation of the additivity rule (AR) was proposed to calculate the total electron scattering cross sections for OCS, O 3, CHCl 3, and C 6H 6. The present calculation covers the range of impact energy from 10 to 2000 eV. The results are compared with experimental data and other theories where available.