Convergent Close-coupling Formalism Research Articles

Vibrational excitation of the state via electron-impact excitation and radiative cascade

Vibrational excitations of are investigated via the electron-impact excitation of the , , , , and states followed by radiative cascade to the vibrational bound and free (continuum) levels of the electronic ground state. The adiabatic-nuclei convergent close-coupling formalism is utilized to calculate cross sections from threshold to 500 eV. Results are in qualitative agreement with previous calculations, however absolute values differ significantly.

Electron scattering from molecular hydrogen in a spheroidal convergent close-coupling formalism

Electron scattering from molecules is a fundamental interaction of matter and is the mechanism behind many chemical reactions. In this work we rework the ab initio Convergent Close-Coupling scattering theory into prolate spheroidal coordinates-a natural system for diatomic molecules-to present total, differential, and ionisation cross sections of electron-H2 collisions.

Two-electron photoionization of ground-state lithium

We apply the convergent close-coupling (CCC) formalism to single-photon two-electron ionization of the lithium atom in its ground state. We treat this reaction as single-electron photon absorption followed by inelastic scattering of the photoelectron on a heliumlike ${\text{Li}}^{+}$ ion. The latter scattering process can be described accurately within the CCC formalism. We obtain integrated cross sections of single photoionization leading to the ground and various excited states of the ${\text{Li}}^{+}$ ion as well as double photoionization extending continuously from the threshold to the asymptotic limit of infinite photon energy. Comparison with available experimental and theoretical data validates the CCC model.

Valence-shell double photoionization of alkaline-earth-metal atoms

We apply the convergent close-coupling formalism to describe direct double photoionization (DPI) of the valence $n{s}^{2}$ shell of alkaline-earth-metal atoms: beryllium $(n=2)$, magnesium $(n=3)$, and calcium $(n=4)$. We consider the range of photon energies below the onset of resonant and Auger ionization processes where the subvalent and core electrons can be treated as spectators. By comparing alkaline-earth-metal atoms with helium, we elucidate the role of the ground state and final ionized state correlations in DPI of various quasi-two-electron atoms.

Differential cross sections for electron impact excitation out of the (…6s6p 1P1) state of barium

Differential cross sections for electron impact on excited state barium atoms have been measured for 20 eV incident electron energy and scattering angles of 5.5°, 9°, 13° and 16°. Results for the excitations (…6s6p 1P1) → X are presented with X = (…6s7s 1S0), (…6s7p 1P1), (…5d2 1D2 + …5d6p 1D2), (…5d2 3P2) and (…6s6d 1D2). Comparisons are made with existing theoretical results calculated in the convergent close coupling formalism and the unitarized distorted wave approximation.

Electron impact coherence parameters for superelastic transitions terminating on the (…6s6p 1P1) level of the barium atom

We have investigated inelastic electron scattering from the laser-excited (…6s6p 1P1) state of barium at 20 eV incident electron energy and scattering angles of 5.5°, 9°, 13° and 16°. Laser excitation with linearly polarized light allowed us to extract P1 and P2 Stokes parameters and the λ parameter for the time-inverse related de-excitations X → (…6s6p 1P1) with X = (…6s7p 1P1), (…6s6d 1D2), (…6s7s 1S0), (…5d2 3P2) and (…5d2 1D2 + …5d6p 1D2). In combination with previously measured values of the P3 Stokes parameter (Johnson P V, Zetner P W, Fursa D and Bray I 2002 Phys. Rev. A 66 22707), we are able to present the set of natural parameters {γ, P+lin, h, P+} for these de-excitations. Comparison of the experimental results with theoretical results calculated in the convergent close coupling formalism is made.

Photoionization with excitation and double photoionization of the helium isoelectronic sequence

We perform a systematic study of photoionization with excitation and double photoionization of ${\mathrm{H}}^{\ensuremath{-}},$ He, and ${\mathrm{Li}}^{+}$ using the convergent close-coupling formalism. The present calculations cover the photon energy range from the double-ionization threshold to 10 keV where the results go over continuously to the nonrelativistic limit of infinite photon energy. By consideration of scaling properties, tested by application to ${\mathrm{O}}^{6+},$ accurate nonrelativistic results for photoionization with excitation to arbitrarily high n and double photoionization may be obtained for all heliumlike targets.

Effect of the ground-state correlations on the helium double photoionization and ionization with excitation

We calculate the helium double photoionization and ionization with excitation cross sections using the convergent close-coupling formalism. We investigate the effect of the ground-state correlations by employing various highly correlated ground-state wave functions: 6-, 10-, and 14-parameter Hylleraas and 7-, 15-, and 18-term multiconfiguration Hartree Fock. As a test of the quality of our calculation, we compare the double to single photoionization cross-section ratio calculated in the three different gauges: length, velocity, and acceleration. We also calculate the partial photoionization cross sections up to $nl~6$ ion excited states and compare them with the latest experimental data. Using the 14-parameter Hylleraas ground state, we obtain almost identical results for the three gauges from the double ionization threshold to 1 keV, and have good agreement with the recent measurements.

Calculation of double photoionization of helium using the convergent close-coupling method.

We use the convergent close-coupling formalism to calculate the double-to-single-photoionization cross-section ratio in helium for photon energies from threshold up to 400 eV. Our results for the velocity and acceleration forms of the electromagnetic interaction operator are very close, and lie in between the measurements of D{umlt o}rner {ital et} {ital al}. [Phys. Rev. Lett. {bold 76}, 2654 (1996)] and Levin {ital et} {ital al}. [Phys. Rev. Lett. {bold 76}, 1220 (1996)]. {copyright} {ital 1996 The American Physical Society.}

Calculation of the total ionization cross section and spin asymmetry in electron-hydrogen scattering from threshold to 500 eV.

We present the total ionization cross section and spin asymmetry at projectile energies ranging from threshold to 500 eV for electron-impact excitation of atomic hydrogen. They are calculated using the convergent close-coupling formalism of Bray and Stelbovics [Phys. Rev. A 46, 6995 (1992)]. Both observables are found to be in complete quantitative agreement with measurements over almost the entire energy range. This is the only electron-atom scattering theory that is able to achieve this result to date.