Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session FT1: Heavy Particle Collisions |
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Chair: Don Madison, Missouri University of Science and Technology Room: Oregon Convention Center A103-A104 |
Tuesday, November 6, 2018 2:00PM - 2:30PM |
FT1.00001: Gas-phase interactions of fast ions and soft X-ray photons with DNA Invited Speaker: Thomas Schlathoelter To improve our understanding of the molecular mechanisms underlying radiation therapy, the interaction of MeV ions and X-ray photons with gas-phase biomolecules has been intensively studied for more than 15 years. Most of the experimental studies were limited to relatively small DNA building blocks. Recently, this limitation was overcome by employing electrospray ionization, to bring large biomolecular systems into the gas phase. In our studies, electrosprayed DNA anions are mass selected and trapped in a radiofrequency ion trap, where they are exposed to MeV ions or to soft X-rays. Even though electron detachment is the dominating channel, DNA damage is clearly observed. We find that this damage prefers to occur at repetitive guanine (G) sequences, as present in human telomeres. The 3D structure of the DNA (linear, duplex, G-quadruplex) is of key relevance for the molecular response. Most relevantly, whereas soft X-ray induced DNA damage is quenched in larger oligonucleotides, MeV ions can always induced base loss and backbone damage, even for large and complex oligonucleotides. [Preview Abstract] |
Tuesday, November 6, 2018 2:30PM - 3:00PM |
FT1.00002: Tuning charge transfer between heavy partners at low scattering energies Invited Speaker: Robin Cote We explore the effect of long-range interactions on neutral-ion collisions and how they can be used to control the outcome of scattering events at low energy. In particular, we explore how the state of the projectile can influence the type of long-range interaction, leading to barriers that reduce or even prevent reactions in some cases, or accentuate the attractive polarization interaction that increase reaction rates in other cases. We discuss results obtained in new types of hybrid traps, where ultracold neutral atoms are overlapping with a crystal of atomic or molecular ions, and in which individual reactions can be detected. We present results on two polyatomic molecular ions reacting with excited Ca atoms, namely BaOCH$_3^+$ and BaCl$^+$. For reactions to take place, Ca needs to be in an excited state, and the reaction rate depends strongly on the spin state of the excited state of Ca, i.e. either $^1P$ or $^3P$. We also discuss a different approach to affect charge exchange in atom-ion collision, namely using Feshbach resonance. This is a different example of using spin-states to affect reactions. Finally, we will present a simple formulation for the charge exchange in the case of resonant processes, linking the s-wave regime to higher temperatures. [Preview Abstract] |
Tuesday, November 6, 2018 3:00PM - 3:15PM |
FT1.00003: Classical description of water molecules in collisions with fast ions Alba Jorge, Marko Horbatsch, Clara Illescas, Tom Kirchner The study of fast ions impinging on molecules of biological interest has become a field of interest in recent years. This is due to a need of atomic data for inelastic processes, involving specifically the water molecule, for hadron therapy. Different theoretical methods, historically used for ion-atom collisions, are being adapted to deal with molecular targets, such as the Classical Trajectory Monte Carlo (CTMC) method, which is being applied for this task using multi-center potentials. However, the non-degeneracy of the molecular orbitals (MOs) and the electron interaction with a non-central potential imply some differences with respect to the atomic approach which need a deeper study. In this work, classical calculations, taking into account the alignment of the initial distribution for each MO, are compared to the quantum-mechanical Two-Center Basis Generator Method and to experimental data, in order to shed light on these issues. [Preview Abstract] |
Tuesday, November 6, 2018 3:15PM - 3:30PM |
FT1.00004: Kinematically Complete Experiment on Double Ionization Accompanied by Capture in Slow He$^{\mathrm{2+}} \quad +$ Ar Collisions Michael Schulz, Yong Gao, DL Guo, Shaofeng Zhang, XL Zhu, RT Zhang, WT Feng, DM Zhao, Xinwen Ma We have performed a kinematically complete experiment on double target ionization accompanied by capture in 120 keV He$^{\mathrm{2+}} \quad +$ Ar collisions. The momentum-analyzed ejected electrons and recoiling target ions were measured in coincidence and the scattered projectile momentum was deduced from momentum conservation. The data were analyzed by several analysis techniques. Fully differential cross sections (FDCS) were extracted to sensitively test theoretical models. 4-particle Dalitz (4-D) plots were analyzed as a tool to combine comprehensiveness with detail. 4-D plots are comprehensive because the integral of the spectrum represents the total cross section. They nevertheless offer a lot of detail as the momentum exchange between all four final-state particles is simultaneously presented in these plots. Finally, the correlation function was generated to identify electron-electron correlations even under conditions, as in this collision system, where such correlations are expected to be very weak. Overall, the data can to a large extent be understood within an independent electron model. However, surprising correlations between the ejected electrons and the scattered projectiles were found. [Preview Abstract] |
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