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

Absolute grand total cross sections for electron scattering from N2 are obtained in the energy range from 20 eV down to 5 meV with very narrow electron energy width of 9 meV using the threshold-photoelectron source. Total cross sections obtained in the present study are compared with the previous experimentally obtained results. At the very-low energy region below 50 meV, the present total cross sections are somewhat smaller than those reported by the Aarhus group [S.V. Hoffmann et al., Rev. Sci. Instrum. 73, 4157 (2002)], which has been the only experimental work that provided the total cross sections in the very-low energy region. The energy positions of the peaks in the total cross sections due to the 2 Π g shape resonance are obtained with higher accuracy, due to the improved uncertainty of the energy position in the present measurement compared to the previous works. The resonance structure in the total cross sections due to the Feshbach resonances of N2 at around 11.5 eV are also observed. Analysis of the resonant structure was carried out in order to determine the values of resonance width of Feshbach resonances of N2.

The absolute total cross section for electron scattering on CH3SH molecules has been measured in a linear electron-transmission experiment for impact energies between 0.6 eV and 250 eV. No theoretical or experimental total cross section data are available for comparison. The obtained total cross section has an energy dependence which is typical for polar molecules. Static electric dipole polarizability of methanethiol has been estimated using a correlation of electron-scattering total cross section with target polarizability. The polarizability of CH3SH thus obtained is in good agreement with values derived by empirical methods.

Absolute total cross sections for electron scattering from He and Ne at electron energies ranging from 6 meV to 20 eV were obtained with the experimental technique employing the threshold-photoelectron source. The measured total cross sections were compared with previous experimental and theoretical cross sections.

Total cross sections of electron scattering by several sulfur-containing molecules OCS, SO2, SF4, SF6, SF5CF3, SO2Cl2 and SO2ClF are calculated at the Hartree-Fork level employing the modified additivity rule approach. The modified additivity rule approach, which was proposed by Shi et al. [Eur. Phys. J. D 45, 253 (2007); Nucl. Instrum. Meth. B 254, 205 (2007)], takes into consideration that the contributions of the geometric shielding effect vary as the energy of incident electrons, the target’s molecular dimension and the atomic and electronic numbers in the molecule. The present investigations cover the impact energies ranging from 30 to 5000 eV. The quantitative total cross sections are compared with those obtained by experiments and other theories. Good agreement is observed even at energies of several tens of eV. It shows that the modified additivity rule approach is applicable to carry out the total cross section calculations of electron scattering by these sulfur-containing molecules at intermediate and high energies, especially over the energy range above 100 eV or so. In the present calculations, the atoms are still represented by the spherical complex optical potential, which is composed of static, exchange, polarization and absorption terms.

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.

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.

The total cross sections for electron and positron collisions with sodium and potassium are calculated in the modified Glauber (MG) approximations, employing the Szazs-McGinn wavefunctions within the frozen-core approach. While the present values of total cross sections for electron and positron collisions are found to be consistent with those previously obtained in the model-potential approach, the positron and electron MG cross sections of the present calculation merge with each other at a rather low energy, as was observed in experiments by Stein et al. (1988-90).

Absolute total electron scattering cross sections for water molecules measured in the 25-300 eV incident energy range using a linear electron transmission device are presented. The results are compared with previous data.

Total cross sections for electron scattering have been measured in the 75--4000-eV energy range for ${\mathrm{NH}}_{3}$, ${\mathrm{SiH}}_{4}$, and ${\mathrm{H}}_{2}$S. For these gases, as well as for ${\mathrm{CH}}_{4}$ and ${\mathrm{H}}_{2}$O, cross sections have been fitted with a Born-like formula containing two parameters for each gas. The high-energy parameter of the fit to the cross sections has been related to the bond length of molecules. Partitioning of total cross sections into inelastic and elastic cross sections for these gases is discussed on the basis of available experimental data.

We report results for positron scattering by ground-state atomic hydrogen in the energy range 0 to 80 eV. The calculations have been performed in an 18-state Ps(1s, 2s, 3s, 4s, 2p, 3p, 4p, 3d, 4d)+H(1s, 2s, 3s, 4s, 2p, 3p, 4p, 3d, 4d) approximation where the pseudostates (denoted by a bar) have been taken from Fon et al. (1981). Cross sections are presented for elastic scattering, positronium formation, total scattering and ionization. The elastic scattering results are in good agreement with accurate variational numbers at low energies and with other sophisticated, but very different, theoretical approximations at higher energies. We estimate that the elastic cross section is now known to better than 10%. The cross section for positronium formation is dominated by capture into the 1s state and is in fairly good agreement with the measurements of Weber et al. (1994). The results for the total cross section are generally consistent with the upper and lower bounds of Zhou et al. (1994) but are a little larger than other theoretical estimates at the higher energies. There is also a general theoretical problem concerning the degree to which the total cross sections for electrons and positrons merge at energies above 31 eV. The calculated ionization cross section is in agreement with the measurements of Jones et al. (1993).

Total cross sections for electron scattering on “quasi spherical” (CH4, SiH4, GeH4) molecules have been analyzed phenomenologically over a wide energy range. Regions, at low and high energies can be usefully represented by simple analytical formulae. Regularities associated with characteristic points such as the Ramsauer minima have been exposed. Comparison with other simple hydrides (NH3, H2O, H2S) allows the demonstration of a possible correlation between the maximum value of the total cross section and the bond length. Some points of contact with first-principles theory are noted and in particular the energy at which the maximum cross section occurs, is related to the occurrence of a partial wave resonance. In the absence of complete data for GeH4, prediction of characteristic points in the low energy cross section proves possible via the phenomenological analysis. Similarly, in the high energy regime, predictions of the cross section for SnH4 is made from data on the lighter molecules of the series, using non-relativistic Thomas-Fermi self consistent field scaling.

In this paper, a recently constructed apparatus for measuring electron scattering cross sections while applying a strong axial magnetic field is utilized for determining total scattering cross sections. The first molecules studied with this setup are pyrimidine (1,3-diazine) and pyrazine (1,4-diazine), whose total cross sections are obtained for the incident electron energy range of 8-500 eV. Quite good agreement with earlier theoretical predictions is found after accounting for the angular acceptance (angular resolution for forward scattering) of the apparatus. However, no other experimental total cross sections for electron scattering from pyrimidine or pyrazine have been found in the literature for comparison.

Absolute total cross section (TCS) for electron scattering from hexafluoroacetone (HFA: (CF3)2CO) molecules has been measured from 1 to 400 eV, employing a linear electron-transmission technique. The TCS energy function for the electron–HFA collision has two broad enhancements: the first, visible between 2 and 28 eV, can be partly attributed to resonant processes; the second is much broader, centred around 50 eV, and is characteristic of perfluorinated targets. The low-energy enhancement is superimposed with weak features perceptible near 3.6, 8.5 and 17 eV. Calculations were carried out for HFA and for acetone to obtain the integral elastic and ionization cross sections at intermediate and high incident energies, using the independent atom approximation and binary-encounter-Bethe approach, respectively. The computed total (elastic plus ionization) cross sections are above 70 eV in reasonable agreement with the experimental TCSs. A comparison is made between cross sections for HFA and its per-hydrogenated counterpart, acetone ((CH3)2CO); the effect of perfluorination is indicated.

The Li–Ar absolute total scattering cross section was measured to an accuracy of 1%–2% over the relative velocity range 1–4× 105 cm/sec, corresponding to relative energies of 0.03–0.5 eV. The absolute cross section determines the radial scale of the interatomic potential, by reference to the average distance between target molecules. The present study is intended as an exemplary system investigation of inferences that can be drawn from more accurate absolute total cross sections, since currently it is believed that this class of total cross section is known to an absolute accuracy of 5%–10% [R. B. Bernstein and J. T. Muckerman, Advan. Chem. Phys. 12, 414 (1967)]. The primary finding is the value of the interatomic potential with an accuracy of about 5% over a span of the relatively large interatomic distances 6–8 Å. At 7 Å the Li–Ar potential is −1.97 × 10−15 erg± 5%. In this region half of the error arises from the systematic error in the cross section and half from the ambiguity about the proper potential model to apply. The results should be useful for critically testing future model potential calculations and, in conjunction with differential scattering and other data, for giving a more exact and complete understanding of the potential. An apparatus was used that had been previously applied to molecule-atom scattering, where angular resolution corrections were negligible and where absolute pressures were measured with a McLeod gauge modified to physically eliminate trap pumping error. A deconvolution procedure that took into account the effects of target motion upon the glory structure of the total cross section was applied to the data. An economical method for applying nonlinear least squares fitting of model interatomic potentials is described and is applied to the data.

In the present study, radiation shielding characteristics of the borogypsum, which is a waste generated during the boric acid production in Turkey, was analyzed. For this purpose, we used recently developed Phy-X/PSD software, which is provided to calculate shielding parameters such as mass attenuation coefficient, linear attenuation coefficient, half-value layer, tenth-value layer, effective atomic number, total atomic cross section, total electronic cross section, effective conductivity, effective electron number, buildup factors and fast neutron removal cross section in a wide photon energy range. Additionally, mass attenuation coefficients of borogypsum were compared with those of other radiation shielding materials (ordinary concrete, obsidian, pumice, clay) in order to give a significant evaluation about the radiation shielding capability of borogypsum. Half value layer and fast neutron removal cross section values are also evaluated by other materials. It is noticed that borogypsum has higher shielding potential than other reported shielding materials.