Bulletin of the American Physical Society
62nd Annual Gaseous Electronics Conference
Volume 54, Number 12
Tuesday–Friday, October 20–23, 2009; Saratoga Springs, New York
Session PW2: Heavy Particle Collisions with Atoms and Molecules |
Hide Abstracts |
Chair: Murtadha Khakoo, California State University, Fullerton Room: Saratoga Hilton Ballroom 2 |
Wednesday, October 21, 2009 1:30PM - 2:00PM |
PW2.00001: Projectile Interactions and Electron Correlation in Four-Body Collisions Invited Speaker: The few-body problem is one of the most fundamental unsolved problems in physics, and arises from the fact that the Schr\"{o}dinger equation is not analytically soluble for more than two mutually interacting particles. As a result, theory must resort to approximations, the validity of which are determined by comparison with experiment. There has been much work done on the three-body problem, and in many cases, theory and experiment agree very well. Recent advancements in experimental techniques and computing capabilities now allow for the study of more complicated collision systems, such as four-body collisions. The simplest four-body problem is a charged particle collision with a helium atom, in which both atomic electrons change state. This type of collision can result in many different outcomes, such as double excitation, excitation-ionization, double ionization, transfer-excitation, transfer-ionization, and double charge transfer. Many body interactions will be discussed in the context of several different four-body processes. [Preview Abstract] |
Wednesday, October 21, 2009 2:00PM - 2:15PM |
PW2.00002: Fully Differential and Double Differential Cross Sections for Single Ionization of H2 by 75 keV Proton Impact Uttam Chowdhury, Michael Schulz, Don Madison We have calculated 3DW-EIS (3 body distorted wave -- Eikonal initial state) fully differential cross sections (FDCS) and doubly differential cross sections (DDCS) for single ionization of H2 by 75 KeV proton impact. Previously published DDCS (differential in the projectile scattering angle and integrated over the ejected electron angles) have found pronounced structures at relatively large angles which were interpreted as an interference resulting from the two-center potential of the molecule. We will investigate the source of these interference effects in the FDCS and examine how interference at the fully differential level can be still observable at the double differential level. [Preview Abstract] |
Wednesday, October 21, 2009 2:15PM - 2:30PM |
PW2.00003: Single Ionization of Atomic Hydrogen by 75 keV Proton Impact Aaron LaForge, Kisra Egodapitiya, Jason Alexander, Michael Schulz, Ahmad Hasan, Marcello Ciappini, Murtadha Khakoo Doubly differential cross sections (DDCS) for single ionization of atomic hydrogen and triple differential cross sections (TDCS) for ionization of molecular hydrogen by 75 keV proton impact have been measured and calculated as a function of the projectile scattering angle and energy loss for the first time. In the case of atomic hydrogen, the data were compared to three theoretical models, each with a different treatment of the nuclear-nuclear interaction. Surprisingly, this comparison reveals that a classical treatment of the nuclear-nuclear interaction is in best agreement with the experimental data. Also, for v$_{el \approx }$v$_{proj}$ the ``post-collision interaction'' (PCI) between the ejected electron and the outgoing projectile ion has a significantly larger effect on the angular distributions of the DDCS than theoretically predicted. [Preview Abstract] |
Wednesday, October 21, 2009 2:30PM - 2:45PM |
PW2.00004: Structures in triply differential cross sections Joseph Macek Triply differential cross sections present the momentum distribution $P${\boldmath $(k)$} of electrons ejected from matter by particle impact. These distributions are used to extract insights about dynamical processes. Unusual, non-smooth, features play important roles in identifying essential features of the atomic dynamics. Our work has found a new source of structure in momentum distributions, namely, vortices in the time-dependent wave function for the dynamical system. We show that these vortices are formed when angular momentum is transferred from relative to internal motion. This angular momentum is normally thought to reside in bound states, however, it can also be carried by electrons ejected from target species. In the latter case the non-zero angular momentum is associated with regions where the electron distribution vanishes. Such regions have ``holes'' in the triply differential cross sections, thus giving rise to new, unexpected structures in electron momentum distributions. We illustrate these structures by calculations of triply differential cross sections for proton and electron impact on atomic species. [Preview Abstract] |
Wednesday, October 21, 2009 2:45PM - 3:00PM |
PW2.00005: Electron Capture in Slow Collisions of Si4+ With Atomic Hydrogen D.C. Joseph, J.P. Gu, B.C. Saha In recent years the charge transfer involving Si4+ and H at low energies has drawn considerable attention both theoretically and experimentally due to its importance not only in astronomical environments but also in modern semiconductor industries. Accurate information regarding its molecular structures and interactions are essential to understand the low energy collision dynamics. Ab initio calculations are performed using the multireference single- and double-excitation configuration-interaction (MRD-CI) method to evaluate potential energies. State selective cross sections are calculate using fully quantum and semi-classical molecular-orbital close coupling (MOCC) methods in the adiabatic representation. Detail results will be presented in the conference. [Preview Abstract] |
Wednesday, October 21, 2009 3:00PM - 3:15PM |
PW2.00006: A nonperturbative quantum mechanical approach to ion-molecule collisions Tom Kirchner, Tobias Spranger, Hans J\"urgen L\"udde A nonperturbative quantum mechanical approach to ion-molecule collisions is presented. Its key ingredients are an expansion of the initially populated molecular orbitals in terms of a single-center basis and a spectral representation of the molecular Hamiltonian. Effectively, the approach amounts to a separation of molecular geometry and collision dynamics and offers the possibility to use well-established ion-atom methods with relatively minor modifications. We apply this rather general approach to ion-water-molecule collisions and calculate cross sections for electron transfer and ionization at impact energies from the few-keV to the few-MeV regime. Different geometries are considered, and the variation of the results with respect to the orientation of the molecule is studied. To compare results with experimental data and other calculations we average the orientation-dependent parts of the Hamiltonian over the three standard Euler angles. This short cut is, of course, an approximation, but first results indicate that it yields reliable total cross sections. [Preview Abstract] |
Wednesday, October 21, 2009 3:15PM - 3:30PM |
PW2.00007: Testing theoretical ion-atom interaction potentials by precise measurements of gas-phase ionic mobilities Rainer Johnsen, Larry Viehland, Timothy Wright In a collaborative effort, we have recently tested \textit{ab-initio} interaction potentials for the ion-atom pairs O$^{+}$-He, O$^{+}$-Ne, O$^{+}$-Ar, He$^{+}$-Ne, and Ne$^{+}$-He by comparing experimental ionic mobilities to those derived from the computed potentials (T. Wright and co-workers) in conjunction with ion transport theory (L. A. Viehland and co-workers). The computed mobilities were then compared to selected-ion drift-tube measurements carried out in the lab of R. Johnsen. Generally, the magnitude and E/n dependences of the calculated mobilities agree with their measured values sufficiently well (within a few percent) to be used with confidence in applications such as discharge modeling, but more accurate mobility measurements (at the 1{\%} or better level) are needed to test for finer details of the interaction, e.g. effects arising from spin-orbit coupling, curve crossings, and the spin state of the ion. Improvements in the experimental apparatus are in progress. We will also present preliminary results on the He$^{+}$-Ar ion-atom pair, for which no previous mobility measurements are available. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700