Project description

The study of the interactions between atoms or molecules and charged particles or intense electromagnetic fields has special practical interest in thermonuclear plasma modeling, astrophysical applications, medical investigations and others. On the other hand, detailed investigations of the electron transition mechanisms in atoms and molecules give us the opportunity to extend our knowledge on properties and dynamics of atomic systems in particular and for complex systems in general.

The project has the following topics:

- Fully differential cross section calculations for atoms and molecules in case of fast ion impact. We plan to improve our semiclassical model by a better description of the projectile scattering.
- Studies of interference effects in ioniozation of diatomic molecules. This topic was intensly studied in the last years both experimentally and theoretically. During this project our aim is to extend the existent studies for the hydrogen molecule to other molecules of practical interest. We also intend to study theoretically the experimentally observed second order interference effects.
- Ionization of atoms and molecules by very short laser pulses. In the context of recent realisations of attosecond laser pulses, the interest for their interactions with atoms and molecules has been increased. We plan to elaborate a theoretical model of the ionization process based on the direct, numerical solving of the time-dependent schrodinger equation. In this way we could treat such cases when the perturbative approximations are not valid. We will study the interference effects of electronic waves appearing in case of the ionization of molecules.
- Ionization of molecules by positron impact. The study of the interactions between positrons and matter are extremely important for medical applications. Our aim is to study beside the direct ionization the positron formation, too.

Objectives of the project

1. For a deep understanding of the correlated dynamics of complex systems with many particles theoretical calculations of the differential cross section for different ionization processes is needed. Discrepancies between experimental data and theoretical results exist, which implies a need of improvement in the present theoretical models. It is important to perform calculation for targets with practical applications, such as the hydrogen molecule.

- The presently used semi-classical model for calculation of differential ionization cross section of the helium atom will be improved. A detailed analysis of the relation between the impact parameter and the momentum transfer as a function of the electron ejection angle will be performed.
- The study of the kinematically complete ionization with excitation of the helium atom. Advanced study of electron correlations, which plays an essential role in two-electron transitions.
- The kinematically complete study of the ionization of the hydrogen molecule will be performed. In the case of the molecules the dynamics of the particles is more complex due to the multi-center potential in which the electrons are moving. Two-center wavefunction will be used to describe the electrons.

2. The previous studies of the interference effects in the ionization of the two-center molecules by charged particle impact will be completed. The previously developed methods for describing the above mentioned phenomena can be applied in a more general manner for every system with an undulatory character.

- The study of the interference effects for the nitrogen molecule will be performed. There are experimental data which suggest that interference effects for the nitrogen molecules are more complex than those obtained for hydrogen molecule. A theoretical description of the ionization process, which takes into account several molecular orbitals is intended and the obtained results will be compared with experimental data.
- The used theoretical model will be improved in order to describe second order effects. The second order approximation of the perturbation theory will be used along with correct wavefunctions for the initial (bound) and final (free) states.

3. The theoretical study of the ionization of the atoms and molecules by intense ultrashort laser pulses will contribute to the better understanding of experiments performed in the last years using cutting edge lasers. Due to the intensity of the used laser fields the theoretical description of the implied processes asks for the direct solution of the time dependent Schrodinger equation.

- The study of the ionization of the hydrogen atom by intense ultrashort laser fields will be performed. The exact numerical solution of the integral equation obtained from the Schrodinger equation will be obtained. The Strong Field Approximation (SFA) will be also used in special cases to simplify the integral equation.
- The ionization of the alkaline atoms by intense ultrashort laser pulses will be also studied. The independent electron approximation will be applied and the Schrodinger will be solved as in the case of the hydrogen atom.
- The interference effects in the ionization of the diatomic molecules by intense ultrashort laser pulses will be analyzed. The two-center character of the studied molecules leads to local maxima and minima in the spectrum of the ejected electrons. These interference effects will be compared with the ones observed and described in the case of the ionization by charged particle impact.
- The ionization of atoms and molecules by charged particle impact in the presence of the external laser fields will be studied. The external laser field strongly influence the spectrum of the ejected electrons and their angular distribution, which influence will be studied in details. The used theoretical model will be similar with the one used in previous cases: the time dependent wavefunction of the studied system will be expanded using as basis set the Volkov wavefunctions. Based on the Schrodinger equation an integral equation for the expansion coefficients will be assembled and will be solved numerically.

4. Using the rich experience accumulated by our group in the study of ionization of molecules by positron impact it is intended to improve the previously used methods. Our area of study will be extended to cover biomedical molecules. This topic presents a strong interdisciplinary character with possible biomedical applications.

- The ionization cross section of the water molecule in positron impact will be calculated. The theoretical calculation implies the expansion of the molecular wavefunctions in terms of spherical functions. The obtained results will be compared with experimental data.
- The formation of positronium during the ionization of diatomic molecules by positron impact will be studied. Positronium formation considerably lowers the ionization threshold and it is a dominant process at low impact energies.
- Cross sections for ionization by positron impact of molecules with biological applications will be calculated. The wavefunctions for these molecules will be ones of Gaussian type, which will be expanded in series as done previously for methane (previously published) or water molecules. The final state of the ejected electron will be given in the framework of the Distorted Wave Born Approximation (DWBA).

Project members

- Director:
- Members:

Results

**1st year (01.10.2007 - 31.12.2007)**

Download Progress Report I.

For this stage of the project the following objectives have been proposed: the study of the interference effects in ionization of the nitrogen molecule; numerical and analytical calculations; the description of the ionization of atoms by ultrashort laser pulses; the construction of a semiclassical model for calculating fully differential cross sections.

During this stage all objectives have been completed.

For a detailed description please download and consult the Progress Report I written in romanian language.

Publications:

- F. Járai-Szabó and L. Nagy, Semiclassical description of kinematically complete experiments, J. Phys. B: At. Mol. Opt. Phys. 40, 4259-4267, 2007
- S. Borbély, K. Tokési and L. Nagy, Ionization of the hydrogen atom by intense ultrashort laser pulses arXiv:0712.0695v1, 2007

**2nd year (01.01.2008 - 15.09.2008)**

Download Progress Report II.

For this stage of the project the following objectives have been proposed: description of the second order interference effects in ionization of diatomic molecules; the ionization of water by positron impact; improved calculations for fully differential ionization cross sections of helium atom.

During this stage all objectives have been completed.

For a detailed description please download and consult the Progress Report II written in romanian language.

Publications:

- J. L. Baran, S. Das, F. Jarai-Szabo, K. Pora, L. Nagy, J. A. Tanis, Suppression of primary electron interferences in the ionization of N
_{2}by 1-5 MeV/u protons, PHYSICAL REVIEW A, 78, 2008, 012710 - K. Pora, L. Nagy, Molecular orientation influence on the interference pattern, Nucl. Instr. Meth. B, 267, 2009, 370-372
- S. Borbely, L. Nagy, Ionization of the hydrogen atom by intense ultrashort laser pulses, PHYSICAL REVIEW A, 77, 2008, 033412
- I. F. Toth, R. I. Campeanu, V. Chis, L. Nagy, Electron impact ionization of diatomic molecules, EUROPEAN PHYSICAL JOURNAL D, 48, 2008, 351-354
- S. Borbely, K. Tokesi, L. Nagy, D. G. Arbo, Over-the-barrier ionization of H
_{2}O by intense ultrashort laser pulses, RADAM 2008 Volume of the International Conference Proceedings Series of the American Institute of Physics, vol. 1080, 2008, 145-150 - F. Jarai-Szabo, L. Nagy, Impact parameter method calculations for fully differential ionization cross sections, arXiv, Atomic Physics, 0810.2904v1 (2008)

**3rd year (16.09.2008 - 15.09.2009)**

Download Progress Report III.

For this stage of the project the following objectives have been proposed: the study of interference effects in ionization of molecules by ultrashort pulses; ionization of diatomic molecules by pozitron impact; positronium formation; cinematically complete study of ionization-excitation by charged particle impact.

During this stage all objectives have been completed.

For a detailed description please download and consult the Progress Report III written in romanian language.

Publications:

- I. Toth, R.I Campeanu, V. Chis, L. Nagy, Distorted-wave Born approximation for the ionization of molecules by positron and electron impact, Nucl. Instr. Meth. B 267 (2009) 362
- F. Jarai-Szabo, L. Nagy, Impact parameter calculations for fully differential ionizations cross sections, Nucl. Instr. Meth. B 267 (2009) 292
- S. Borbely, K. Tokesi, L. Nagy, Interaction of intense short laser pulses with positronium, Nucl. Instr. Meth. B 267 (2009) 386
- F. Jarai-Szabo, K Pora, L. Nagy, Semiclassical model for calculating fully differential ionization cross sections of the H
_{2}molecule, J. Phys. B: At. Mol. Opt. Phys. 42 (2009) 245203, arXiv:0908.2340 - S. Borbely, K. Pora and L. Nagy, Non-perturbative investigation of the interference effects in the ionization of the H
_{2}by charged particle impact, Journal of Physics: Conference Series 163 (2009) 012067 - S. Borbely, G.Zs. Kiss, L. Nagy, The excitation and ionization of the hydrogen atom in strong laser field, Central European Journal of Physics 8 (2009) 249-257
- S. Borbely, K. Tokesi, L. Nagy and D. G. Arbo, Ionization of the H
_{2}O molecule by intense ultrashort laser pulses, Journal of Physics: Conference Series 194 (2009) 032044 - F. Jarai-Szabo and L. Nagy, Semiclassical fully differential cross section calculations for the ionization of small molecules, Journal of Physics: Conference Series 194 (2009) 102037

**4th year (16.09.2009 - 15.09.2010)**

Download Progress Report IV.

For this stage of the project the following objectives have been proposed: Description of spatial and temporal interferences in ionization produced by multiple laser pulses; ionization of organic molecules by pozitron impact; study of ionization of atoms by charged particle impact in intense laser fields.

During this stage all objectives have been completed.

For a detailed description please download and consult the Progress Report IV written in romanian language.

Publications:

- S. Borbély, L. Nagy, K. Tőkési, Ionization of the water by intense ultrashort half-cycle electric pulses, Eur. J. Phys. D 59 (2010) 337
- D. G. Arbó, M. S. Gravielle, K. I. Dimitriou, K. Tőkési, S. Borbély and J. E. Miraglia, Ionization of the hydrogen atom by short half-cycle pulses: dependence on the pulse duration, Eur. Phy. J. D 59 (2010) 193
- I. Toth, R. I. Campeanu, V. Chis, L. Nagy, Ionization of the water molecule by electron and positron impact, Journal of Physics: Conference Series 199 (2010) 012018
- I. Toth, L. Nagy, Triple-differential cross-section calculations for the ionization of CH4 by electron impact, J. Phys. B: At. Mol. Opt. Phys. 43 (2010) 135204
- A. Toth, I. Toth, L. Nagy, Calculated totally differential cross sections for the ionization of helium by electron impact, Studia Universitatis Babes-Bolyai, Phyisica, LIV, 2, 2009
- D. G. Arbó, M. S. Gravielle, K. Tőkési, S. Borbély, K. Dimitriou and J. E. Miraglia, Atomic ionization by ultrashort half-cycle pulses, J. Phys. Conf. Ser. 194 (2009) 022030
- S. Borbély, L. Nagy, K. Tőkési, D. G. Arbó, M. S. Gravielle, J. E. Miraglia Bound electron states role in the ionization of atoms, ECAMP10 (10th European conference on Atoms, Molecules and Photons), Salamanca, Spania, 4-10 julie 2010
- L. Nagy, I. Tóth, Theoretical triple differential cross sections for the ionization of the CH4 by electron impact, ECAMP10, Salamanca, Spania, 4-10 julie 2010

Involvment of young researchers

All young researchers have substantial contribution to the analytical and numerical calculations carried out in the project.

All three PhD students involved in the project have finished the PhD studies by defending in public their PhD Thesis written in the topic of the project.