Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session PR5: Electron Collisions with Atoms and Molecules I |
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Chair: Tom Rescigno, Lawrence Berkeley National Laboratory Room: Village Square |
Thursday, October 3, 2013 1:30PM - 2:00PM |
PR5.00001: Large-scale B-spline R-matrix calculations of electron impact excitation and ionization processes in complex atoms Invited Speaker: Oleg Zatsarinny In recent years, the B-spline R-matrix (BSR) method [1] has been applied to the treatment of a large number of atomic structure and electron-atom collision problems. Characteristic features of the BSR approach include the use of B-splines as a universal basis to describe the projectile electron inside the R-matrix box and the employment of term-dependent, and hence non-orthogonal, orbitals to construct the target states. The latter flexibility has proven to be of crucial importance for complex targets with several partially filled subshells. The published computer code [2] has since been updated and extended to allow for a fully relativistic description at the level of the Dirac-Coulomb hamiltonian. Also, the systematic inclusion of a large number of pseudo-states in the close-coupling expansion has made it possible to extend the range of applicability from elastic and inelastic low-energy near-threshold phenomena to intermediate energies (up to several times the ionization threshold) and, in particular, to describe ionization processes as well. The basic ideas of the BSR approach will be reviewed, and its application will be illustrated for a variety of targets. Particular emphasis will be placed on systems of relevance for applications in gaseous electronics, such as the generation of complete datasets for electron collisions with the heavy noble gases Ne-Xe. Many of our data, which are needed for the description of transport processes in plasmas, are available through the LXCat database [3].\\[4pt] [1] O. Zatsarinny and K. Bartschat. J. Phys. B {\bf 46} (2013) 112001.\\[0pt] [2] O. Zatsarinny, Comp. Phys. Commun. {\bf 174} (2006) 273.\\[0pt] [3] http://www.lxcat.laplace.univ-tlse.fr/database.php [Preview Abstract] |
Thursday, October 3, 2013 2:00PM - 2:15PM |
PR5.00002: Electron Impaction Ionisation from Laser Aligned Magnesium Kate Nixon, Andrew Murray, Gregory Armstrong, James Colgan Very recently, major advances have been made in theoretical predications of electron impact ionisation from molecular targets at low energies [1]. This has been achieved by averaging a number of cross sections, each calculated for a discrete target orientation. The accuracy of the individual cross sections is however still untested. Obtaining experimental data for molecular targets of a known orientation is difficult, and has only been achieved in a few studies for diatomic molecules [2-4]. Atomic targets can also be used to characterise the influence of alignment on the electron impact ionisation. In these studies laser radiation excites an atom to a P state and, more importantly, control the orientation of the electron density within the atom, as demonstrated by Nixon and Murray [5]. New experimental results for magnesium will be presented where the target alignment is varied within the scattering plane. These results will be accompanied by theoretical predictions from new time dependant close coupling (TDCC) calculations.\\[4pt] [1] D Madison, personal communications\\[0pt] [2] M Takahashi et al. 2005 PRL 94 213202\\[0pt] [3] A Senftleben et al. 2010 J. Chem. Phys. 133 1\\[0pt] [4] S Bellm, et al. 2010 PRL 104 023202\\[0pt] [5] KL Nixon and AJ Murray 2011 PRL 106 12320 [Preview Abstract] |
Thursday, October 3, 2013 2:15PM - 2:30PM |
PR5.00003: Triple Differential Cross Sections for Ionization of Laser-Aligned Mg Atoms by electron impact Sadek Amami, Don Madison, Kate Nixon, Andrew Murray 3DW (3-body distorted wave) triple differential cross sections have been calculated for electron impact ionization of magnesium atoms aligned by lasers. Calculations have been performed for the kinematics of the experiment performed by Kate Nixon and Andrew Murray at Manchester, England [K. L. Nixon and A. J. Murray 2011 Phys. Rev. Lett. 106, 123201]. An incident projectile was produced with energy of 41.91eV, scattered and ejected electrons were detected with equal energies (E1$=$E2$=$20eV), the scattered projectile was detected at a fixed angle of 30deg, and the ejected electrons were detected at angles ranging between 0$^{\mathrm{o}}$ -- 180$^{\mathrm{o}}$. The theoretical 3DW results will be compared with the experimental data. [Preview Abstract] |
Thursday, October 3, 2013 2:30PM - 3:00PM |
PR5.00004: Accuracy of Theoretical OAMO Calculations for Electron-Impact Ionization of Molecules Invited Speaker: Hari Chaluvadi The study of electron impact single ionization of atoms and molecules has provided valuable information about fundamental collisions. The most detailed information is obtained from triple differential cross sections (TDCS) in which the energy and momentum of all three final state particles are determined. These cross sections are much more difficult for theory since the detailed kinematics of the experiment become important. There are many theoretical approximations for ionization of molecules. One of the successful methods is the distorted wave (DW) approximation. One of the strengths of the DW approximation is that it can be applied for any energy and any size molecule. One of the approximations that has been made to significantly reduce the required computer time is the OAMO (orientation averaged molecular orbital) approximation. Surprisingly, the M3DW-OAMO approximation yields reasonably good agreement with experiment for ionization of H$_{2}$ by both low and intermediate energy incident electrons. On the other hand, the M3DW-OAMO results for ionization of CH$_{4}$ [1,2] and NH$_{3}$ [3] did not agree very well with experiment. Consequently, we decided to check the validity of the OAMO approximation by performing a proper average over orientations and we found much better agreement with experimental data. In this talk we will show the current status of agreement between experiment and theory for low and intermediate energy single ionization of small, medium, and large molecules.\\[4pt] [1] Nixon et al 2012 J.Chem. Phys. 136 094302\\[0pt] [2] Xu et al 2012 J. Chem. Phys. 137 024301\\[0pt] [3] Nixon et al 2013 J. Chem. Phys. 138 174304 [Preview Abstract] |
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