Near-threshold positron-impact ionization of atomic hydrogen

We consider the positron-impact ionization (breakup) of atomic hydrogen utilizing the full and S-wave model calculations, concentrating on the near-threshold energy region. Unlike the corresponding electron-impact case, the S-wave model does support the Wannier-like threshold law predicted by Ihra et al. [Phys. Rev. Lett. 78, 4027 (1997)10.1103/PhysRevLett.78.4027]. It is found that convergent S-wave model cross sections are obtained only if complete expansions are utilized on both the atomic and the positronium centers. Furthermore, we suggest that, in the model and full calculations, the separate contributions to the breakup cross section from both centers become equal at threshold.     

The effect of target representation in positron-impact ionization of molecular hydrogen

Ionization cross sections for positron collisions with hydrogen molecules have been calculated using a two-center molecular representation. The results are compared with our previous work which used sphericaly averaged H₂ wavefunctions as well as with existing experimental results. The use of a two-centre wave function for the molecular target, either of the Heitler–London type or a Gaussian representation, produces results which lie between the two most recent sets of experimental data. We find that our CPE4 model produces results in better agreement with experiment over the whole energy range than our CPE model.     

Experimental ionization of atomic hydrogen with few-cycle pulses

We present experimental data on strong-field ionization of atomic hydrogen by few-cycle laser pulses. We obtain quantitative agreement at the 10% level between the data and an ab initio simulation over a wide range of laser intensities and electron energies.     

Electron-impact ionization of atomic hydrogen: dynamical variational treatment

A simple and straightforward calculating scheme is proposed for electron-impact single and multiple ionization of atoms. The method is based on the application of the Hulthén-Kohn dynamical variational principle. An effective charge seen by the scattered electron is determined for a certain type of trial wave functions mathematically in a rigorous way excluding any empirical assumptions. Validity of the elaborated approach is assessed by calculating triply differential cross section (TDCS) for electron-impact ionization of hydrogen. It is shown that, inclusion of the effective charge into the calculation reduces height of a “binary peak” in comparison with the first Born approximation result. The height of a “recoil peak” depends on the sign of the effective charge. The calculated TDCS are compared with the available experimental data and with the results of sophisticated theories and agreement is found.     

Positron impact ionization of atomic hydrogen at low energies

Low energy positron impact ionization of atomic hydrogen is studies theoretically using the hyperspherical partial wave method of Das [1] in constant Θ₁₂, equal energy sharing geometry. The TDCS reveal considerable differences in physics compared to electron impact ionization under the same geometry.     

Resonant ionization of atomic hydrogen as a source of polarized protons

The method of obtaining polarized proton beams by means of resonant ionization of the hydrogen atoms is considered. The main physical features of the phenomenon are discussed. The conditions are found in which the degree of proton polarization is equal to 100%. The optimum values are found of the pulse duration and the field strengths of the exciting and ionizing light waves.     

Emergence of classical orbits in few-cycle above-threshold ionization of atomic hydrogen

The time-dependent Schr?dinger equation for atomic hydrogen in few-cycle laser pulses is solved numerically. Introducing a positive definite quantum distribution function in energy-position space, a straightforward comparison of the numerical ab initio results with classical orbit theory is facilitated. Integration over position space yields directly the photoelectron spectra so that the various pathways contributing to a certain energy in the photoelectron spectra can be established in an unprecedented direct and transparent way.     

Photoelectron angular distributions and energy spectra of atomic hydrogen in above threshold ionization

Abstract

We extend our model for two-color above threshold ionization to include an infinite number of continua, which are labeled by their angular momenta. Results are presented for the photoelectron spectra and the angular photoelectron distributions.     

Modified over-barrier model for ionization cross sections of atomic hydrogen by multiply charged ions

The impact ionization of atomic hydrogen in collisions with H⁺, He²⁺, Li2,3+, C2,3,4,5,6+, N2,3,4,5+, O2,3,4,5,6+, and Ar3,4,5,6+ ions has been studied by the modified over-barrier model at low-to-intermediate velocities. Compared with the calculated results of the classical trajectory Monte Carlo (CTMC) method and the unitarized-distorted-wave approximation (UDWA), this model satisfactorily reproduces the experimentally obtained velocity dependence of the absolute ionization cross sections at intermediate impact velocities.     

Laser-assisted particle-atom ionization. Analysis of triple and double differential cross-sections

Summary Based on a theoretical model worked out previously, an analysis is reported of triplet and double differential cross-section of hydrogen atom ionization by electron impact in the presence of a single-mode, homogeneous, linearly polarized, off-resonance laser field. In particular, calculations are carried out to investigatea) the dependence of the cross-sections on the field strength,b) the average number of exchanged photons,c) the limits of validity of a known sum rule. The reported results improve considerably the present knowledge of this kind of elementary stimulated atomic process. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Monte Carlo determination of the field dependence of the first Townsend ionization coefficient for atomic hydrogen

The Monte Carlo method has been used to find the /p₀ = f(E/p₀) dependence for atomic hydrogen from E/p₀ = 10 to 100 V/cm-torr· For the calculation it was assumed that elastic collisions and ionization could be accompanied by an atomic excitation corresponding to the transition of a ls electron to a 2s or 2p level.Translated from Izvestiya VUZ. Fizika, No. 8, pp. 70–76, August, 1970.In conclusion the authors thank R. K. Peterkop for moral support of the fundamental idea of this paper.     

Spectroscopy of atomic hydrogen

This article presents a review of the most recent theoretical and experimental results in hydrogen. We particularly emphasize the methods used to deduce the Rydberg constant R _∞ and we consider the prospects for future improvements in the precision of R _∞.     

Electron and positron impact ionization of atomic hydrogen and helium using CPB approximation with post-collision interaction

Triple differential cross-sections for the electron and positron impact ionization of atomic hydrogen and helium are calculated in a first order model using a product of two Coulomb wavefunctions for the final state continuum electrons supplemented by post-collision interaction effects.     

Massively parallel ionization of extended atomic systems

Massively parallel ionization of many atoms in a cluster or biomolecule is identified as a new phenomenon of light-matter interaction which becomes feasible through short and intense FEL pulses. Almost simultaneously emitted from the illuminated target the photo-electrons can have such a high density that they interact substantially even after photoionization. This interaction results in a characteristic electron spectrum which can be interpreted as a convolution of a mean-field electron dynamics and binary electron-electron collisions. We demonstrate that this universal spectrum can be obtained analytically by summing synthetic two-body Coulomb collision events. Moreover, we propose an experiment with hydrogen clusters to observe massively parallel ionization.     

Thermodynamics of Bose-condensed atomic hydrogen

We study the thermodynamics of the Bose-condensed atomic hydrogen confined in the Ioffe-Pritchard potential. Such a trapping potential, that models the magnetic trap used in recent experiments with hydrogen, is anharmonic and strongly anisotropic. We calculate the ground-state properties, the condensed and non-condensed fraction and the Bose-Einstein transition temperature. The thermodynamics of the system is strongly affected by the anharmonicity of this external trap. Finally, we consider the possibility to detect Josephson-like currents by creating a double-well barrier with a laser beam. Received 15 February 2000     

Muonium/muonic hydrogen formation in atomic hydrogen

The muonium/muonic hydrogen atom formation in μ^±−H collisions is investigated, using a two-state approximation in a time dependent formalism. It is found that muonium cross-section results are similar to the cross-section results obtained for positronium formation in e⁺-H collision. Muonic hydrogen atom formation cross-sections in μ^--H collision are found to be significant in a narrow range of energy (5 eV–25 eV).