Work with Tom Kirchner and Hans Juergen Luedde and postdoc Mitsuko Murakami on ion-molecule collisions
ions on water molecules: book chapter: link Advances in Quantum Chemistry 65 (2013) 315-337.
protons on water molecules: net cross sections: PDF Phys. Rev. A 80, 060702(R) (2009).
protons on water molecules: charge-state correlated and fragmentation: PDF Phys. Rev. A 85, 052704 (2012).
protons on water molecules: developing a fragmentation model: PDF Phys. Rev. A 85, 052713 (2012).
He+(1s) on water molecules: charge-state correlated and fragmentation: PDF Phys. Rev. A 86, 022719 (2012).
Work with Mitsuko Murakami on high harmonic generation using a 3d code to deal with mutually orthogonal linearly polarized two-color laser fields:PDF Phys. Rev. A 88, 063419 (2013).
York Sept 2014 talk: 2-color HHG and electron momentum distributions for H(1s) exposed to elliptic and circularly polarized few-cycle laser pulses, including the attoclock set-up:PDF .
Work with Mitsuko Murakami and Tom Kirchner on high harmonic generation by molecules in a two-dimensional (reduced geometry) model: PDF Can J Phys 90, 537 (2012).
Work with Tom Kirchner and Gerald Schenk on projectile electron contributions in B2+ on Ne collisions: PDF Phys. Rev. A 88, 012712 (2013).
Work with Eric A. Hessels, and Alain Marsman on the lineshape problem.
Shifts from a distant neighboring resonance (3-level atom) PDF Phys. Rev. A 82, 052519 (2010).
Shifts from a distant neighboring resonance (4-level atom) PDF Phys. Rev. A 84, 032508 (2011).
Shifts in microwave measurements of n=2 triplet He fine structure PDF Phys. Rev. A 86, 012510 (2012).
Shifts in laser measurements of n=2 triplet He fine structure PDF Phys. Rev. A 86, 040501(R) (2012).
Shifts in saturated fluorescence spectroscopy of n=2 triplet He fine structure PDF Phys. Rev. A 89, 043403 (2014).
Work with Wendy Taylor on liquid argon scintillator respones to highly ionizing particles
Birks' law correction: PDF NIM A 664,111 (2012).
Work with Alain Marsman on supercritical Dirac resonances.
Coupled differential equations approach to resonance calculations: PDF Phys. Rev. A 84, 032517 (2011).
Work with Ts Tsogbayar on Stark resonances using the Fourier grid and pseudospectral methods.
2d-calculations with complex absorber PDF Few-Body Systems 2012
The DC Stark problem for the molecular hydrogen ion H2+ PDF J. Phys. B 46, 085004 (2013)
The AC Stark problem for the molecular hydrogen ion H2+ in the low frequency limit and its connection to the DC Stark problem PDF J. Phys. B 46, 245005 (2013)
High harmonic generation from the hydrogen molecular ion H2+ at low continuous-wave laser frequencies in a Floquet approach. PDF J. Phys. B 47, 115003 (2014)
Work with Eric A. Hessels and Michael W. Horbatsch on classical calculation of radiative decays.
Lifetimes and branching ratios for field-free hydrogenic atoms: PDF Phys. Rev. A 71, 020501(R) (2005).
Scaling behavior of the quantum lifetimes on the basis of a correspondence principle between QED and classical electromagnetism: PDF J. Phys. B 38, 1765-71 (2005).
Classical calculation of lifetimes of hydrogenic atoms in a magnetic field: PDF Phys. Rev. A 72, 033405 (2005).
Work with Eddie Ackad on the mapped Fourier grid method applied to the Dirac equation
Paper on solving the stationary Dirac equation with a mapped Fourier grid method:(Eddie Ackad's M.Sc. work) PDF J. Phys. A 38, 3157-71 (2005).
Paper on supercritical Dirac resonances by complex scaling or absorbing potential technique with a mapped Fourier grid method:(part of Eddie Ackad's PhD work) PDF Phys. Rev A 75, 022508 (2007).
Paper on coupled-channel supercritical Dirac resonances by smooth exterior scaling or absorbing potential technique and Pade extrapolation: (part of Eddie Ackad's PhD work) PDF Phys. Rev A 76, 022503 (2007).
Progress Report for ICPEAC 2007 (Freiburg) on coupled-channel S-P-D supercritical Dirac resonances and dynamical positron production in bare U-U collisions at the Coulomb barrier: (part of Eddie Ackad's PhD work) PDF Journal of Physics: Conference Series 88, 012017.
Paper on positron-electron pair production in heavy ion collisions at the Coulomb barrier: PDF Phys. Rev. A 78, 062711 (2008).
Talk at SPARC 2009 (Lisbon) on positron production in bare U-U collisions at the Coulomb barrier: (with Dr. Eddie Ackad and graduate/summer students) PDF (slides)
Paper on trapping of atoms in a cylindrical geometry using van der Waals force combined with evanescent near-resonant laser light in a hollow optical fiber: PDF J. Mod. Optics 49, 2555-63 (2002).
Work with Andrei Terekidi and Jurij Darewych on QED
Lande g-factor calculation for hydrogen-like excited states in muonium PDF , Phys Rev A 75, 043401 (2007)
Relativistic two-fermion wave equation PDF , Can. J. Phys., in press (2007)
Paper on 50-60 keV proton-hydrogen collisions (for M. Chassid's PhD) PDF Phys. Rev. A 66, 012714 (2002).
Work on ion-atom collisions with more than one electron using density functional theory. Collision energies are in the tens of keV to one thousand keV (or keV/amu). This work is done in collaboration with Tom Kirchner (YorkU, and TU Clausthal) and Hans-Juergen Luedde (Frankfurt) and uses the optimized potential model for atomic structure.
Review Article (Dec. 2003) for Recent Research Developments in Physics (Research Signpost, Kerala, India) : ps . PDF .
protons on oxygen: PDF Phys. Rev. A 61, 052710 (2000).
He++ on neon: PDF Phys. Rev. A 62, 042704 (2000).
C4+ on neon: PDF Phys. Rev. A 64, 012711 (2001).
He+(1s) on neon: PDF Phys. Rev. A 63, 062718 (2001).
highly charged ions on argon: PDF Phys. Rev. A 62, 022702 (2000).
protons, alphas, antiprotons on argon: PDF Phys. Rev. A66, 052719 (2002).
antiprotons on helium: PDF J. Phys. B 35, 925-34 (2002).
State-selective capture in proton-argon collisions: PDF Phys. Rev. A69, 012708 (2004).
Tom Kirchner's progress report presented at ICPEAC 2003 (Physica Scripta 2004): PDF
Coupled mean-field description of He+ -Ne and He+ -Ar (poster for DPG): PDF(colour) paper: PDF J. Phys. B 37, 2379-85 (2004).
Hans-Juergen Luedde's progress report presented at ICPEAC 2001 (Rinton Press 2002): PDF(colour)
A publication list as of May 2005 in PDF form.
Cartoons to illustrate proton-hydrogen collisions:These gif-movies are from 1998. For best viewing use an old computer with at least 1024*768 pixel resolution. They depict results from numerical calculations for ion-atom collisions using the FFT split-operator technique. Cross section results from this method were published in 2002 in PRA. Previous numerical work on protons on hydrogen was published in a Denton-conference proceeding (AIP Conference Proceedings 392, page 71. That work was carried out with a Crank-Nicholson integrator, and the paper was rejected by Phys. Lett. A in 1996).
The current results are from an early version of our FFT code where the numerics were restricted to 256*128*64 points. The work under review in PRA uses 256*256*128 and 256^3 - sized meshes on which we can remove the n=1,2,3 shell contributions. We have acceptable total cross sections, and for ionized electron energies above 10 eV probably the best theoretical doubly-differential cross sections available. Preprints can be requested by sending mail to firstname.lastname@example.org
The densities shown in the gif-movies are integrated over the direction perpendicular to the theoretical scattering plane. We show some total densities to explain how our center-of-charge reference fram works: the neutral atom carries the initial density from left to right into the collision, while the impinging ion moves right-to-left. They both move with half the impact speed.
Here are 3 impact parameters for a velocity of 0.5 v_Bohr, i.e., 6.25 keV impact energy. The ionized part is hard to see, because the bound parts dominate the total density, but one can see a part of the cloud left stranded in the saddle region at the end.
b=1 v=0.5 p-H
b=2 v=0.5 p-H
b=3 v=0.5 p-H
Here are 2 impact parameters for a velocity of 0.75 v_Bohr, i.e., 14.06 keV impact energy. The ionized electron density is shown, but it also includes n=3 excitations [we didn't dare to project them out on the small mesh]. One sees the different behavior for the 2 impact parameters
b=4 v=0.75 p-H total density in scattering plane
b=2 v=0.75 p-H ionized density
b=4 v=0.75 p-H ionized density
The low-energy results obtained on the small meshes are problematic, in particular, as substantial amounts of density accumulate around the nuclei. For higher collision energies (50 keV, v=1.414) we are more confident, and we show also momentum distributions from the p-space wavefunction, which asymptotically become the ionized electron momentum distributions. The change in the final phases of the collision for those electrons that still experience a Coulomb attraction to one of the nuclei, i.e., these electrons are still losing kinetic energy as they move away from a Coulomb centre.
The densities show how the ionization density is formed in the centre of charge, but somewhat closer to the target nucleus. Therefore, the momentum distribution which is initially centred in the CM frame moves as the target atom reclaims control over the ionized electrons, i.e., they don't remain in the centre. For slower collisions the ionized electrons remain close to the centre of charge (mass). For larger impact parameters the ionized density has momenta closer to the target atom, but in our time-dependent picture this involves a time evolution as well! The Born-approximation enthusiasts (CDW included) and experimentalists will have a hard time to understand this.
b=0.5 v=1.414 p-H ionized electron density in p/x spaces
b=1 v=1.414 p-H ionized electron density in p/x spaces
b=2 v=1.414 p-H ionized electron density in p/x spaces
b=3 v=1.414 p-H ionized electron density in p/x spaces
b=4 v=1.414 p-H ionized electron density in p/x spaces
b=6 v=1.414 p-H ionized electron density in p/x spaces
Classical Trajectory calculations using an energy-window distribution function as an initial state carried out by Vladimir Pletnev and Marko Horbatsch. They show marked differences to the quantum calculations: phase space is quite restrictive as to where classical particles are allowed to be: a sphere in r-space around the nuclei is left empty. In p-space the range of small momenta is only allowed at very large asymptotic times.
b=3 v=2.135 p-H ionized electron scatterplot in p/x spaces