LINE INTENSITIES AND MOLECULAR OPACITIES OF THE FeH F ^4Delta~i-X ^4Delta~i TRANSITION

Electron transfer processes in ${\mathrm{He}}^{+}+\mathrm{He}$ collisions are studied theoretically using a three-electron semiclassical atomic-orbital close-coupling method in a wide energy domain, from 1 to 225 keV/u. Total, state-selective, and angular-differential cross sections are presented and compared with available experimental and theoretical results. A prominent oscillatory energy dependence structure in the transfer-excitation cross sections is observed and explained by a strong competition between these channels and the projectile-excitation processes. Moreover, the angular-differential cross sections considered in this work exhibit an oscillatory structure which is interpreted within a Fraunhofer-type diffraction model. For the two highest considered collision energies, the cross sections show a different pattern for which both Fraunhofer-type diffraction and the Thomas mechanism have to be advocated.

State-selective electron transfer in He + +He collisions at intermediate energies

We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. Roadmap III focusses on heavy particles: with zer ...

https://iopscience.iop.org/article/10.1088/1361-6455/ab26ea/pdf

Roadmap on photonic, electronic and atomic collision physics: III. Heavy particles: with zero to relativistic speeds

We use the two-center wave-packet convergent close-coupling approach to calculate singly differential cross sections for direct scattering, electron capture, and ionization in proton-hydrogen collisions at intermediate energies. The distinct feature of the approach is that it gives a complete differential picture of all the interconnected processes at once, subject to the unitary principle. Results obtained for the angular differential cross sections of elastic scattering, excitation, and electron capture, as well as the ionization cross sections differential in the ejected-electron angle, and in the ejected-electron energy agree well with available experimental data. It is concluded that the two-center wave-packet convergent close-coupling approach is capable of providing a realistic differential picture of all collision processes taking place in proton-hydrogen collisions.

Singly differential cross sections for direct scattering, electron capture, and ionization in proton-hydrogen collisions

Calculations of ionization and electron-capture cross sections in ion-atom collisions usually require solving the Schro dinger equation governing the collision system by expanding the total scattering wave function in a basis of target- and projectile-centered pseudostates. This approach leads to the two-center close-coupling equations which in some cases may become ill-conditioned due to the non-orthogonality of the underlying combined basis. Here we develop a technique which allows to accurately extract the necessary collision information, including that for the rearrangement channels, from the computationally more convenient one-center close-coupling equations which are built from only target-centered pseudostates. The robustness of the method is demonstrated by considering the proton-hydrogen scattering problem across a wide incident energy range. The developed method is then applied to study proton scattering on multielectron target of lithium. The obtained results for the 2s → 2p excitation and the total electron-capture cross sections are in good agreement with corresponding experimental data. It is concluded that the presented technique could be a simpler alternative when integrated cross sections are required.

One-center close-coupling approach to two-center rearrangement collisions

The electron-capture processes in ${\mathrm{C}}^{4+}$ + He collisions have been studied theoretically using a two-active-electron semiclassical atomic-orbital close-coupling method in a wide energy domain. The results of the present calculations are compared with available theoretical predictions and experimental measurements: very good agreements are found for both total and state-selective single-electron-capture (SEC) and double-electron-capture (DEC) cross sections. We extend the understanding on that system to high energies for which only a single series of data exists. Furthermore, the mechanisms responsible for SEC and DEC processes have been investigated by additional restricted two-active-electron and single-active-electron calculations. The role of electronic correlations in the collisions is also discussed.

Single- and double-electron transfer in low- and intermediate-energy C 4 + + He collisions

Molecular Opacity Calculations for Lithium Hydride at Low Temperature

We have investigated the double electron capture process in the ${\mathrm{H}}^{+}+{\mathrm{H}}^{\ensuremath{-}}$ collision system for energies from 60 eV to 20 keV. Despite the apparent simplicity of this highly correlated system, all previous calculations fail to reproduce the experimental total cross sections. Moreover, the latter exhibit oscillations that have been previously attributed to quantum interferences between the gerade and ungerade ionic states of the transient molecule formed during the collision. For this process, we present the absolute cross sections obtained from a fully correlated two-active-electron semiclassical atomic-orbital close-coupling approach. Our results reproduce well the experimental data in both magnitude and shape. Furthermore, we demonstrate that the oscillations stem from coherence effects between double electron capture and other two-electron inelastic channels, namely the transfer-excitation processes. This alternative interpretation is supported by a Rosenthal-like model based on a molecular treatment of the collision. Our results shed new light on this old but challenging problem.

Double Electron Capture in H + +H - Collisions

Two-body fragmentation of ${\mathrm{N}}_{2}{\mathrm{O}}^{q+}$ ($q=2,3$) induced by electron-capture collision of $5.7\ensuremath{-}\mathrm{keV}/\mathrm{u}\phantom{\rule{0.28em}{0ex}}\mathrm{X}{\mathrm{e}}^{15+}$ is studied. Through the triply coincident measurement on ion-pair fragments with the scattered projectile and the correlation analysis on the ion-pair time of flight and momentum conservation, we have clearly identified 12 reaction channels for the formation and dissociation of ${\mathrm{N}}_{2}{\mathrm{O}}^{2+}$ and ${\mathrm{N}}_{2}{\mathrm{O}}^{3+}$. The fraction ratios for these channels and the corresponding kinetic energy release (KER) distributions for the ion-pair products have been obtained. Calculations of the potential energy curves of ${\mathrm{N}}_{2}{\mathrm{O}}^{3+}$ for the N-N and N-O bond stretches are performed using the complete active space self-consistent field method. The KER spectra for the two-body fragmentation of ${\mathrm{N}}_{2}{\mathrm{O}}^{2+}\ensuremath{\rightarrow}{\mathrm{N}}^{+}+\mathrm{N}{\mathrm{O}}^{+}$ and $\mathrm{N}{{}_{2}}^{+}+{\mathrm{O}}^{+}$ can be explained by the decay via the $X\phantom{\rule{0.28em}{0ex}}^{3}\mathrm{\ensuremath{\Sigma}}^{\ensuremath{-}}$ and $1\phantom{\rule{0.28em}{0ex}}^{3}\mathrm{\ensuremath{\Pi}}$ states, and the major peaks or structures observed in the KER spectra for ${\mathrm{N}}_{2}{\mathrm{O}}^{3+}\ensuremath{\rightarrow}{\mathrm{N}}^{+}+\mathrm{N}{\mathrm{O}}^{2+}$ can be attributed to the $1\phantom{\rule{0.28em}{0ex}}^{2}\mathrm{\ensuremath{\Pi}}, 2\phantom{\rule{0.28em}{0ex}}^{2}\mathrm{\ensuremath{\Pi}}$, and $2\phantom{\rule{0.28em}{0ex}}^{2}\mathrm{\ensuremath{\Sigma}}^{\ensuremath{-}}$ states, whereas those in the KER spectra for ${\mathrm{N}}_{2}{\mathrm{O}}^{3+}\ensuremath{\rightarrow}{\mathrm{O}}^{+}+{\mathrm{N}}_{2}^{2+}$ are mainly contributed from the $1\phantom{\rule{0.28em}{0ex}}^{2}\mathrm{\ensuremath{\Pi}}, 3\phantom{\rule{0.28em}{0ex}}^{2}\mathrm{\ensuremath{\Pi}}$, and $4\phantom{\rule{0.28em}{0ex}}^{2}\mathrm{\ensuremath{\Pi}}$ states. In addition, we found that the KER structures for the same ion-pair products are not sensitive to the number of electrons stabilized at the projectile, but the KER intensities are clearly dependent on it. The mechanism of multielectron captures of the projectile to form the transient multicharged molecular ions and the following projectile stabilization with or without autoionizing cascades is proposed to explain it.

J. G. Wang

Papers

State-selective electron transfer in He + +He collisions at intermediate energies

Single- and double-electron transfer in low- and intermediate-energy C 4 + + He collisions

Molecular Opacity Calculations for Lithium Hydride at Low Temperature

Double Electron Capture in H + +H - Collisions

Two-body fragmentation dynamics of N 2 O q + ( q = 2 , 3 ) induced by electron-capture collisions with 5.7 − keV / u X e 15 +