Luca Chiari

Tokyo University of Science, Edo, Tōkyō, Japan

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Publications (57)128.48 Total impact

  • Antonio Zecca, Luca Chiari
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    ABSTRACT: Resonances in positron scattering from several atomic and molecular species are predicted by theoretical models. However, only positron-molecule binding was experimentally confirmed so far. Sharp structures in positron total cross sections were also measured; however, their detection is still in a very preliminary stage owing to instrumental limitations. Here we briefly review the present knowledge about structures in low-energy positron scattering. Based on further measurements and re-analysis of the experimental data collected at the University of Trento, we also present evidence of sharp structures in the total cross sections for several atomic and molecular targets. We find that the behaviour of some of those features can be described using the equation of a Fano resonance line-shape, despite the fact that an actual resonant scattering process might not be involved. Possible mechanisms that can give rise to such structures still need to be identified. Further independent experimental work using high-resolution spectrometers is needed in order to confirm the existence of structures in positron scattering cross sections.
    Molecular Physics 05/2015; DOI:10.1080/00268976.2015.1046524 · 1.64 Impact Factor
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    ABSTRACT: Quantitative information about positron and electron collisions with nucleobases is required in charged-particle track simulations to accurately model and assess any radiation damage at the subcellular level in biological systems. However, scattering experiments have so far been restricted to the pyrimidine nucleobases. In this paper we report on total-cross-section measurements for positron impact on indole, a parent molecule of the purine nucleobases, at impact energies between 1 and 25 eV. We also present theoretical cross sections for elastic and total scattering, positronium formation, electronic excitations, and direct ionization between 1 and 500 eV, as calculated with the independent-atom model with the screening-corrected additivity rule. Rotational excitation cross sections are additionally calculated within a Born framework over that same energy range. A significant discrepancy is found between the measured and computed total cross sections, which cannot be entirely accounted for by the lack of forward-angle-scattering discrimination in the experiment. The present results are also compared to the available theoretical cross sections for the purine nucleobases. In addition, total cross sections for electron-indole collisions computed within our theoretical formalism are provided.
    Physical Review A 01/2015; 91(1). DOI:10.1103/PhysRevA.91.012711 · 2.99 Impact Factor
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    ABSTRACT: We have measured (e,2e) triple differential cross sections (TDCS) for the electron-impact ionisation of phenol with coplanar asymmetrical kinematics for an incident electron energy of 250 eV. Experimental measurements of the angular distribution of the slow outgoing electrons at 20 eV are obtained when the incident electron scatters through angles of -5°, -10°, and -15°, respectively. The TDCS data are compared with calculations performed within the molecular 3-body distorted wave model. In this case, a mixed level of agreement, that was dependent on the kinematical condition being probed, was observed between the theoretical and experimental results in the binary peak region. The experimental intensity of the recoil features under all kinematical conditions was relatively small, but was still largely underestimated by the theoretical calculations.
    The Journal of Chemical Physics 09/2014; 141(12):124307. DOI:10.1063/1.4896072 · 3.12 Impact Factor
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    ABSTRACT: Using a Beer–Lambert attenuation approach, we report measured total cross sections (TCSs) for positron scattering from vinyl acetate (C4H6O2) in the incident positron energy range 0.15–50 eV. In addition, we also report an independent atom model with screening corrected additivity rule computation results for the TCSs, differential and integral elastic cross sections, the positronium formation cross section and inelastic integral cross sections. The energy range of these calculations is 1–1000 eV. While there is a reasonable qualitative correspondence between measurement and calculation for the TCSs, in terms of the energy dependence of those cross sections, the theory was found to be a factor of ~2 larger in magnitude at the lower energies, even after the measured data were corrected for the forward angle scattering effect.
    Journal of Physics B Atomic Molecular and Optical Physics 08/2014; 47(17):175202. DOI:10.1088/0953-4075/47/17/175202 · 1.92 Impact Factor
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    ABSTRACT: We present experimental electron-energy loss spectra (EELS) that were measured at impact energies of 20 and 30 eV and at angles of 90° and 10°, respectively, with energy resolution ∼70 meV. EELS for 250 eV incident electron energy over a range of angles between 3° and 50° have also been measured at a moderate energy resolution (∼0.9 eV). The latter spectra were used to derive differential cross sections and generalised oscillator strengths (GOS) for the dipole-allowed electronic transitions, through normalization to data for elastic electron scattering from benzene. Theoretical calculations were performed using time-dependent density functional theory and single-excitation configuration interaction methods. These calculations were used to assign the experimentally measured spectra. Calculated optical oscillator strengths were also compared to those derived from the GOS data. This provides the first investigation of all singlet and triplet excited electronic states of phenol up to the first ionization potential.
    The Journal of Chemical Physics 08/2014; 141(7):074314. DOI:10.1063/1.4893116 · 3.12 Impact Factor
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    ABSTRACT: Measurements of the grand total and total positronium formation cross sections for positron scattering from uracil have been performed for energies between 1 and 180 eV, using a trap-based beam apparatus. Angular, quasi-elastic differential cross section measurements at 1, 3, 5, 10, and 20 eV are also presented and discussed. These measurements are compared to existing experimental results and theoretical calculations, including our own calculations using a variant of the independent atom approach.
    The Journal of Chemical Physics 07/2014; 141(3):034306. DOI:10.1063/1.4887072 · 3.12 Impact Factor
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    ABSTRACT: We report on measurements of differential cross sections (DCSs) for electron impact excitation of a series of Rydberg electronic-states in α-tetrahydrofurfuryl alcohol (THFA). The energy range of these experiments was 20-50 eV, while the scattered electron was detected in the 10°-90° angular range. There are currently no other experimental data or theoretical computations against which we can directly compare the present measured results. Nonetheless, we are able to compare our THFA DCSs with earlier cross section measurements for Rydberg-state electronic excitation for tetrahydrofuran, a similar cyclic ether, from Do et al. [J. Chem. Phys. 134, 144302 (2011)]. In addition, "rotationally averaged" elastic DCSs, calculated using our independent atom model with screened additivity rule correction approach are also reported. Those latter results give integral cross sections consistent with the optical theorem, and supercede those from the only previous study of Milosavljević et al. [Eur. Phys. J. D 40, 107 (2006)].
    The Journal of Chemical Physics 07/2014; 141(2-2):-. DOI:10.1063/1.4885856 · 3.12 Impact Factor
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    ABSTRACT: We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of Rydberg electronic-states in α-tetrahydrofurfuryl alcohol. The energy range of these experiments was 20–50 eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely for the total cross section, elastic ICS, inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. Where possible, our calculated cross sections are compared to the limited available data of each scattering process.
    Chemical Physics Letters 07/2014; 608:161–166. DOI:10.1016/j.cplett.2014.05.087 · 1.99 Impact Factor
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    ABSTRACT: Differential and integral cross section measurements, for incident electron energies in the 20-50 eV range, are reported for excitation of several composite vibrational modes in α-tetrahydrofurfuryl alcohol (THFA). Optimisation and frequency calculations, using GAUSSIAN 09 at the B3LYP/aug-cc-pVDZ level, were also undertaken for the two most abundant conformers of THFA, with results being reported for their respective mode classifications and excitation energies. Those calculations assisted us in the experimental assignments of the composite features observed in our measured energy loss spectra. There are, to the best of our knowledge, no other experimental or theoretical data currently available in the literature against which we can compare the present results.
    The Journal of Chemical Physics 06/2014; 140(21):214306. DOI:10.1063/1.4879779 · 3.12 Impact Factor
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    ABSTRACT: We present experimental and theoretical results for the electron-impact ionization of the highest occupied molecular orbitals of tetrahydropyran and 1,4-dioxane. Using an (e,2e) technique in asymmetric coplanar kinematics, angular distributions of the slow ejected electron, with an energy of 20 eV, are measured when incident electrons at 250 eV ionize the target and scatter through an angle of either -10° or -15°. The data are compared with calculations performed at the molecular 3-body distorted wave level. Fair agreement between the theoretical model and the experimental measurements was observed. The similar structures for these targets provide key insights for assessing the limitations of the theoretical calculations. This study in turn facilitates an improved understanding of the dynamics in the ionization process.
    The Journal of Chemical Physics 06/2014; 140(21):214312. DOI:10.1063/1.4880204 · 3.12 Impact Factor
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    ABSTRACT: The electronic spectroscopy of isolated tetrahydrofurfuryl alcohol (THFA) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.0-10.8 eV energy-range, with absolute cross-section measurements derived. The He(I) photoelectron spectrum was also collected to quantify ionisation energies in the 9-16 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground and excited state of the positive ion. The good agreement between the theoretical results and the measurements allows us to quantify for the first time the electronic state spectroscopy of THFA. The present work also considers the question of the lowest energy conformers of the molecule and its population distribution at room temperature.
    The Journal of Physical Chemistry A 04/2014; 118(33). DOI:10.1021/jp501634w · 2.78 Impact Factor
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    ABSTRACT: We present new cross section results from a joint experimental and theoretical investigation into low-energy positron and electron scattering from two targets of biological interest, namely tetrahydrofuran and 3-hydroxy-tetrahydrofuran. We compare and discuss the total, elastic and inelastic cross sections for these species in the light of potential positron and electron-induced damage in biomolecular systems.
    Journal of Physics Conference Series 04/2014; 488(7):072007. DOI:10.1088/1742-6596/488/7/072007
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    ABSTRACT: We report on differential cross section results for low-energy electron collisions with the biologically relevant species a-tetrahydrofurfuryl alcohol. Electron-impact excitation measurements of the electronic states of a-tetrahydrofurfuryl alcohol were carried out at incident energies between 15-50 eV and for scattering angles in the range 20-90°. Elastic differential cross section have also been calculated within the Independent Atom Model and using the Screening Corrected Additivity Rule approach at selected energies between 1-1000 eV.
    Journal of Physics Conference Series 04/2014; 488(5):052003. DOI:10.1088/1742-6596/488/5/052003
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    ABSTRACT: Experimental and theoretical cross sections are presented for electron-impact ionization of a series of cyclic ethers.
    Journal of Physics Conference Series 04/2014; 488(5):052004. DOI:10.1088/1742-6596/488/5/052004
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    ABSTRACT: 2,2,4-Trimethylpentane (C8H18), a hydrocarbon produced all over the world on a large scale in the processing of crude oil, has long been known and used in the energy sector. It has also recently attracted the attention of the radiation physics and chemistry community, owing to its applications in medical imaging techniques. Charged-particle interactions with this species unfortunately remain mostly unknown. In this study, we report on measured total cross sections for positron scattering from 2,2,4-trimethylpentane in the energy range from 0.12 to 50 eV. We also present calculations of the total cross sections, elastic integral and differential cross sections, positronium formation cross sections and inelastic integral cross sections at energies from 1 to 1000 eV using the Independent Atom Model with Screening Corrected Additivity Rule. A knowledge of those scattering cross sections might, through simulation models, help to improve the accuracy of current radiation detection devices and hence provide better estimates of the extent of any charged-particle-induced damage in biomolecular systems.
    The Journal of Physical Chemistry A 03/2014; 118(33). DOI:10.1021/jp502632m · 2.78 Impact Factor
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    ABSTRACT: We present and discuss recent results, both experimental and theoretical (where possible), for electron impact excitation of the 3s[3/2]1 and 3s'[1/2]1 electronic states in neon, elastic electron scattering from the structurally similar molecules benzene, pyrazine, and 1,4-dioxane and excitation of the electronic states of the important bio-molecule analogue α-tetrahydrofurfuryl alcohol. While comparison between theoretical and experimental results suggests that benchmarked cross sections for electron scattering from atoms is feasible in the near-term, significant further theoretical development for electron-molecule collisions, particularly in respect to discrete excitation processes, is still required.
    02/2014; 1588(1). DOI:10.1063/1.4866925
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    ABSTRACT: Utilising a high-resolution, trap-based positron beam, we have measured both elastic and inelastic scattering of positrons from water vapour. The measurements comprise differential elastic, total elastic, and total inelastic (not including positronium formation) absolute cross sections. The energy range investigated is from 1 eV to 60 eV. Comparison with theory is made with both R-Matrix and distorted wave calculations, and with our own application of the Independent Atom Model for positron interactions.
    The Journal of Chemical Physics 12/2013; 140(4). DOI:10.1063/1.4862685 · 3.12 Impact Factor
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    ABSTRACT: Total cross section (TCS) measurements for positron scattering from nitrogen dioxide (NO2) are presented in the energy range 0.2-40 eV. The TCS, the elastic integral and differential cross sections, and the integral cross section accounting of all the inelastic processes (including positronium formation) have also been computed using the independent atom model with screening corrected additivity rule (IAM-SCAR) for incident energies from 1 to 1000 eV. A qualitative level of agreement is found between the present TCS experiment and theory at the common energies. As no previous measurements or calculations for positron-NO2 scattering exist in the literature, we also computed the TCS for electron collisions with NO2 employing the IAM-SCAR method. A comparison of those results to the present positron cross sections and the earlier electron-impact data and calculations is provided. To investigate the role that chemical substitution plays in positron scattering phenomena, we also compare the present positron-NO2 data with the TCSs measured at the University of Trento for positron scattering from N2O and CO2.
    Journal of Physics B Atomic Molecular and Optical Physics 12/2013; 46(23):5202-. DOI:10.1088/0953-4075/46/23/235202 · 1.92 Impact Factor
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    ABSTRACT: We present cross-section results from an experimental and theoretical study on positron scattering from nitrous oxide. Total cross sections (TCSs) have been measured at incident energies between 0.1 and 70 eV with a linear-transmission-based positron spectrometer. Elastic differential and integral cross sections, as well as inelastic integral cross sections and TCSs, have been computed with two different theoretical approaches: the independent atom model with screening-corrected additivity rule (IAM-SCAR), at energies in the 1- to 1000-eV range, and the Schwinger multichannel method at energies between 0.1 and 10 eV. Note that the latter method specifically reports cross sections for the elastic channel. We find good qualitative agreement between the theories and the TCS experiment at all common energies. That level of accord is found to also become quantitative above the ionization energy of nitrous oxide. Electron-impact TCSs calculated with the IAM-SCAR approach are also presented and compared to the existing results in order to uncover any similarities or differences in the scattering processes between these two leptons and nitrous oxide.
    Physical Review A 08/2013; 88(2). DOI:10.1103/PhysRevA.88.022708 · 2.99 Impact Factor

Publication Stats

396 Citations
128.48 Total Impact Points

Institutions

  • 2015
    • Tokyo University of Science
      Edo, Tōkyō, Japan
  • 2013–2014
    • Australian National University
      • Research School of Physics & Engineering
      Canberra, Australian Capital Territory, Australia
  • 2012–2014
    • Flinders University
      • School of Chemical and Physical Sciences
      Tarndarnya, South Australia, Australia
  • 2008–2013
    • Università degli Studi di Trento
      • Department of Physics
      Trient, Trentino-Alto Adige, Italy