A M Ermolaev

Neutralisation and detachment in collisions between protons and negative hydrogen ions in the proton energy range from 0.62 to 80.0 keV lab

New theoretical cross sections are reported for neutralisation, detachment and production of hydrogen in collisions between H+ and H- ions in the energy range from 0.62 to 80.0 keV lab. Close-coupled calculations were carried out, within the semiclassical (impact parameter) approximations, with the wavefunction expanded in terms of a two-centre basis of travelling atomic orbitals with up to 51 states. For low energies (E 10 keV lab, the main contribution (for neutralisation only) comes from the core electron. The total cross sections are then obtained by applying a modified version (Ermolaev) of the independent-particle model. There is an excellent agreement with experiment in a wide range of energies.

Theoretical study of the n=2 excitation of atomic hydrogen by proton impact

The n=2 excitation of atomic hydrogen by proton impact has been studied using the semiclassical impact parameter coupled-channel method in the range of impact energies between 15 and 1000 keV. In the discussion that follows, special attention is paid to the interval from 15 to 200 keV where theoretical cross sections show considerable variation depending on the particular choice of the expansion basis and where experimental data for excitation of the 2p subshell have recently become available.

Direct excitation, ionisation and energy loss in proton-atomic-hydrogen collisions at impact energies from 30 keV to 5 MeV

As a preliminary part of an investigation of the proton/antiproton interactions with matter, semiclassical impact parameter cross sections for direct excitation and ionisation of atomic hydrogen by proton impact have been computed in a wide energy range from 30 keV to 5 MeV. The coupled-state calculations used a 51-state two-centre atomic orbital expansion. The computed cross sections are in excellent agreement with available experimental data. Calculations of energy loss for protons moving in a gas of atomic hydrogen are also reported.

Charge transfer in H+-Na0 collisions: atomic orbital calculations

Cross sections have been computed for the charge transfer processes H++Na(3s) to H(nl)+Na+, with n=1, n=2 and n=3, and for H(1s)+Na+ to H++Na(3l), with l=0, l=1 and l=2. the laboratory energy range studied was 0.5<or=E<or=20 keV amu-1. A two-centre expansion in travelling atomic orbitals was employed. Comparison is made, where possible, with other calculations and with experiment. For H+-Na collisions, good agreement is found over the entire energy range with recent atomic orbital calculations by Fritsch (1984) and with the earlier measurements of Anderson et al. (1979). Agreement with molecular orbital calculations reported by Allan (1986) in an accompanying paper is also good for energies E<5 keV amu-1. The computed values of the Na 3s to 3p excitation cross section are given.

Charge exchange between Cs+ ions and related studies

The two-state approximation in the impact parameter formalism, using atomic basis functions with plane-wave translational factors, is used to compute cross sections for the charge exchange reaction Cs++Cs+ to Cs+Cs2+ for energies from 300 keV to 5 MeV. To test certain aspects of the model, calculations are presented for the reactions Li++Li+ to Li+Li2+, H++He to H+He+ and H++Li+ to H+Li2+, in the intermediate-energy regions.

Remarks on current tests of quantum electrodynamics for two-electron ions

Current calculations of the Lamb shifts and relativistic corrections for two-electron ions are critically analysed and the need for reliable values of average excitation energies k0 for two-electron ions over a wide range of states and Z is re-emphasised.

Study of He+-H collisions at intermediate keV energies using psuedo-oneand two-electron atomic orbital expansions

We report a theoretical study of excitation, charge transfer and ionization in collisions between helium ions He+ and atomic hydrogen in the impact energy range between 2.5 and 250 keV amu-1. The colliding system was treated in a full two-electron formulation as well as in a pseudo-one-electron approximation to the total Hamiltonian. The wavefunctions were expanded in terms of two-centre atomic orbital bases within the semiclassical impact parameter close-coupling method. The results demonstrate advantages and limitations of either approach and allow a detailed comparison to be made with a wide range of available experimental data.

Charge transfer in He2++Li collisions

Cross sections for single-electron capture by He2+ from the L- and K-shells of Li atoms are computed in a wide range of energies between 1.9 keV and 1.6 MeV (lab) using the same atomic orbital expansion method and numerical techniques as those described in the companion paper by Ermolaev. It is confirmed that the preferential capture of the 2s electron from Li into the n=3 states of He+ persists for energies as high as 40-65 keV (lab). The present calculations also confirm that an experimentally observed high-energy shoulder in the total capture cross sections is due to an increasing importance, for energies of 100 keV and higher, of the capture of the K-shell electrons from Li. For low energies (1.9-5 keV) the computed cross sections are considerably lower than those recently calculated by Fritsch and Lin. This disagreement highlights the necessity of further theoretical and experimental studies of the reaction in this low-energy region.

Neutralization of protons in energetic collisions with hydrogen-like beryllium ions

A theoretical study of hydrogen production in collisions between protons and hydrogen-like beryllium ions Be3+ is reported, for a proton impact energy range between 100 keV and 3 MeV. Cross sections are obtained in close-coupled atomic-orbital calculations within the semiclassical impact parameter method. The presented results are relevant to design and interpretation of current experiments at JET where a substantial flux of neutral hydrogen is observed to be generated at the centre of the tokamak plasma.

Quantal and classical calculations of He2++Li interactions at intermediate energies. I. Charge transfer

The authors report a comparative study of the quantal and classical treatments of single-electron charge transfer from the L and K shells of Li(1s22s) in collision with He2+ ions at intermediate energies. Quantal calculations have been performed using coupled-state atomic orbital expansions with up to 43 pseudostates in the basis, within the impact parameter formalism, for impact energies of 8 to 2000 keV lab. Classical trajectory Monte Carlo calculations for L-shell capture, using a model potential for the active electron, have been performed for impact energies from 50 to 400 keV, and using an effective-charge model for K-shell capture at impact energies from 600 to 2000 keV lab.