Positron scattering from molecular hydrogen

We present results for total and partial cross sections for positron scattering from H2. The total scattering and positronium formation cross sections are reported between 0.5 and 200 eV. Total quasielastic and inelastic scattering cross sections are rep

Absolute elastic differential cross sections for electron scattering by C6H5CH3 and C6H5CF3 at 1.5–200 eV: a comparative experimental and theoretical study with C6H6

We present absolute differential cross sections DCS for elastic scattering from two benzene derivatives C6H5CH3 and C6H5CF3. The crossed-beam method was used in conjunction with the relative flow technique using helium as the reference gas to obtain absolute values. Measurements were carried out for scattering angles 15° –130° and impact energies 1.5–200 eV. DCS results for these two molecules were compared to those of C6H6 from our previous study. We found that 1 these three molecules have DCS with very similar magnitudes and shapes over the energy range 1.5–200 eV, although DCS for C6H5CF3 increase steeply toward lower scattering angles due to the dipole moment induced long-range interaction at 1.5 and 4.5 eV, and 2 that the molecular structure of the benzene ring significantly determines the collision dynamics. From the measured DCS, elastic integral cross sections have been calculated. Furthermore, by employing a corrected form of the independent-atom method known as the screen corrected additive rule, DCS calculations have been carried out without any empirical parameter fittings, i.e., in an ab initio nature. Results show that the calculated DCS are in excellent agreement with the experimental values at 50, 100, and 200 eV

Experimental and theoretical cross sections for positron collisions with 3-hydroxy-tetrahydrofuran

Cross section results from a joint experimental and theoretical investigation into positron scattering from 3-hydroxy-tetrahydrofuran (3H-THF) are presented. Total and positronium (Ps) formation cross sections have been measured from 1 to 190 eV using the positron beamline at the Australian National University, which has an energy resolution between 60 and 100 meV. The total cross section (TCS) and the elastic and total inelastic integral cross sections in the energy range between 1 and 1000 eV have been computed within the Independent Atom Model using the Screening Corrected Additivity Rule approach. In addition, we have calculated elastic differential cross sections at selected incident energies. Our computations represent the first theoretical results reported for this target species, while our measured Ps formation cross sections are also novel. Comparison of the present TCS with the previous results from the University of Trento shows a good level of agreement at the lowest energies. We also provide a comparison between the present cross sections for 3H-THF and those from our earlier study on the parent molecule tetrahydrofuran.The authors acknowledge the Australian Research Council (ARC) Centres of Excellence Program for funding. C.M. is also grateful to the ARC for financial support under the Australian Postdoctoral Fellowship program. G.G. and F.B. would like to acknowledge the Spanish Ministerio de Economía y Productividad (Project FIS2009-10245) and the European Science Foundation (COST Action MP1002 – Nano-IBCT) for financial support

Total and positronium formation cross sections for positron scattering from H2O and HCOOH

Total and positronium formation cross sections have been measured for positron scattering from H2O and HCOOH using a positron beam with an energy resolution of 60 meV (full-width at half-maximum (FWHM)). The energy range covered is 0.5–60 eV, including an investigation of the behavior of the onset of the positronium formation channel using measurements with a 50 meV energy step, the result of which shows no evidence of any channel coupling effects or scattering resonances for either molecule

Experimental and theoretical cross sections for positron collisions with 3-hydroxy-tetrahydrofuran

Cross section results from a joint experimental and theoretical investigation into positron scattering from 3-hydroxy-tetrahydrofuran (3H-THF) are presented. Total and positronium (Ps) formation cross sections have been measured from 1 to 190 eV using the positron beamline at the Australian National University, which has an energy resolution between 60 and 100 meV. The total cross section (TCS) and the elastic and total inelastic integral cross sections in the energy range between 1 and 1000 eV have been computed within the Independent Atom Model using the Screening Corrected Additivity Rule approach. In addition, we have calculated elastic differential cross sections at selected incident energies. Our computations represent the first theoretical results reported for this target species, while our measured Ps formation cross sections are also novel. Comparison of the present TCS with the previous results from the University of Trento shows a good level of agreement at the lowest energies. We also provide a comparison between the present cross sections for 3H-THF and those from our earlier study on the parent molecule tetrahydrofuran

Low-energy positron interactions with xenon

Low-energy interactions of positrons with xenon have been studied both experimentally and theoretically. The experimental measurements were carried out using a trap-based positron beam with an energy resolution of ̃80 meV, while the theoretical calculat

Total, elastic, and inelastic cross sections for positron and electron collisions with tetrahydrofuran

We present total, elastic, and inelastic cross sections for positron and electron scattering from tetrahydrofuran (THF) in the energy range between 1 and 5000 eV. Total cross sections (TCS), positronium formation cross sections, the summed inelastic integral cross sections (ICS) for electronic excitations and direct ionization, as well as elastic differential cross sections (DCS) at selected incident energies, have been measured for positron collisions with THF. The positron beam used to carry out these experiments had an energy resolution in the range 40–100 meV (full-width at half-maximum). We also present TCS results for positron and electron scattering from THF computed within the independent atom model using the screening corrected additivity rule approach. In addition, we calculated positron-impact elastic DCS and the sum over all inelastic ICS (except rotations and vibrations). While our integral and differential positron cross sections are the first of their kind, we compare our TCS with previous literature values for this species. We also provide a comparison between positron and electron-impact cross sections, in order to uncover any differences or similarities in the scattering dynamics with these two different projectiles

Similarities and differences between electron and positron scattering from molecules

In this paper a comparative study is carried out between total cross sections (TCS) for electron impact with those for positron impact using both experimental and theoretical procedures. The method used for the measurements is a retarding potential time-of-flight (RP-TOF) while the theoretical procedure is the Continuum Multiple Scattering (CMS) model. The experimental energy range is 0.2-1000 eV while that for the CMS is 1.5-100 eV. For polar molecules, the increase in TCS observed below 2 eV is expected due to the dipole induced long range interaction that has been observed only for some molecules for electron impact. In the energy range 3-60 eV electron TCS are characteristically larger than positron TCS due to resonances in the former. Some peculiar cases have been studied whereby positron TCS become unexpectedly greater than electron TCS at energies below 10 eV. The first Born approximation has been observed to hold for the impact energy region above a few hundred of eV for all molecules studied in this laboratory, albeit with different threshold energies

High-resolution, low-energy positron scattering from helium: measurements of the total scattering cross section

We present high-resolution (80 meV FWHM) measurements of the positron-helium total cross section in the energy range between 1 and 15 eV. The absolute magnitude of the cross section is in excellent agreement with recent state-of-the-art theoretical calculations and with previous absolute measurements (e.g. Mizogawa et al). Specific scans in the 1-3 eV and 5-8 eV energy regions reveal no evidence of the structures in the cross section reported by Karwasz et al

Low energy positron scattering from helium A

Positron scattering from helium has been historically limited to experiments with energy resolution of 0.5 eV or worse. A new apparatus has been developed that allows the investigation of scattering processes with an energy resolution as good as 30 meV, allowing new experimental insight into positron helium interactions. High resolution measurements of low energy scattering from helium will be presented, with a particular emphasis on the development of benchmark cross sections, the investigation of threshold behaviour and the search for positron scattering resonances