Quantum-mechanical Molecular-orbital Close-coupling Research Articles

Single- and double-electron capture processes in low-energy collisions of N3+with He

Single-electron capture (SEC) and double-electron capture (DEC) processes in collisions of ground state N{sup 3+} (2s{sup 2} {sup 1}S) ions with He are investigated by using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. The ab initio adiabatic potentials, radial and rotational coupling matrices utilized in QMOCC calculations, are obtained from the multireference single- and double-excitation configuration interaction approach. Total and state-selective SEC and DEC cross sections are presented in the low-energy range from 0.1 eV to 15 keV (i.e., 0.007 eV/u -1.07 keV/u) and rate coefficients in the temperature range from 10{sup 4} to 10{sup 7} K. Our results indicate that the SEC dominates the charge-transfer process in the considered energy region of this collision system and the SEC cross sections are nearly constant in the relatively high-collision energy region, while the DEC cross sections are about 2 orders of magnitude smaller. It is found that, for the SEC processes, in the dominant mechanisms, electrons are captured to exoergic channels N{sup 2+} (2s2p{sup 2} {sup 2}D,{sup 2}S), and for the DEC processes, they are captured to N{sup +} (2s{sup 2}2p{sup 2} {sup 1}D,{sup 1}S). Our calculations also reveal that rotational couplings become important at E > 10 eV/u for SEC andmore » E > 200 eV/u for DEC processes.« less

Cross sections for electron capture in H+-Li(2pσ,π±) collisions

State-selective and total single-electron-capture cross sections in collisions of H${}^{+}$ with the excited Li${}^{*}$(2p) atom have been investigated by using the full quantum-mechanical molecular orbital close-coupling (QMOCC) method in the energy range 0.001--3 keV/u and by the two-center atomic orbital close-coupling (TC-AOCC) method in the energy range 0.1--100 keV/u. The present results are also compared with data from other sources when available. It is found that the total and partial electron-capture cross sections are sensitive to the initial p-state charge cloud alignment, particularly in the low-energy region.

Theoretical investigation of charge transfer between N6+and atomic hydrogen

Charge transfer due to collisions of ground-state N{sup 6+}(1s{sup 2} S) with atomic hydrogen has been investigated theoretically using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method, in which the adiabatic potentials and nonadiabatic couplings were obtained using the multireference single- and double-excitation configuration-interaction (MRDCI) approach. Total, n-, l-, and S-resolved cross sections have been obtained for energies between 10 meV/u and 10 keV/u. The QMOCC results were compared to available experimental and theoretical data as well as to merged-beams measurements and atomic-orbital close-coupling and classical trajectory Monte Carlo calculations. The accuracy of the QMOCC charge-transfer cross sections was found to be sensitive to the accuracy of the adiabatic potentials and couplings. Consequently, we developed a method to optimize the atomic basis sets used in the MRDCI calculations for highly charged ions. Since cross sections, especially those that are state selective, are necessary input for x-ray emission simulation of heliospheric and Martian exospheric spectra arising from solar wind ion-neutral gas collisions, a recommended set of state-selective cross sections, based on our evaluation of the calculations and measurements, is provided.

Quantum-mechanical calculations of charge transfer in collisions ofO3+with He

Charge transfer due to collisions of ground-state ${\text{O}}^{3+}(2{s}^{2}2p\text{ }^{2}P)$ ions with He is investigated using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. The ab initio adiabatic potentials and radial couplings utilized in the QMOCC calculations are obtained from the multireference single- and double-excitation configuration interaction approach. State-selective and total charge-transfer cross sections are calculated for collision energies from 0.01 eV/u to 1 keV/u. Comparison with existing data reveals that the present QMOCC calculations are in good harmony with the measured total single-electron charge-transfer cross sections. Excellent agreement with the available experimental data is also found for state-selective cross sections at the measured energy region.

Charge transfer and excitation in slow proton collisions with sodium

The charge transfer and excitation cross sections for protons colliding with $\mathrm{Na}(3s)$ atoms are calculated in the incident energy region from $1.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}5\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ by a quantum-mechanical molecular-orbital close-coupling (QMOCC) method and from $1\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}100\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ by a two-center atomic-orbital close-coupling method. The present QMOCC charge transfer cross section for low energy $(<40\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ is in agreement with some other calculations, but disagrees with the experimental measurements [Z. Phys. A 313, 155, 1983]. For the higher energies, the cross sections calculated by the two methods are in harmony with the experimental and other theoretical data.

Quantum-mechanical calculations of vibrationally resolved cross sections for non-dissociative charge transfer of O3+ with H2

Charge transfer due to collisions of ground state O3+(2s22p 2P) ions with molecular hydrogen is investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) method，and electronic and vibrational state-selective cross sections along with the corresponding differential cross sections are calculated for projectile energies of 100，500，1000 and 5000eV/u at the orientation angles of 25°，45° and 89°. The adiabatic potentials and radial coupling matrix elements utilized in the QMOCC calculations were obtained with the spin-coupled valence-bond approach. The infinite order sudden approximation (IOSA) and the vibrational sudden approximation (VSA) are utilized to deal with the rotation of H2 and the coupling between the electron and the vibration of H2. It is found that the distribution of vibrationally resolved cross sections with the vibrational quantum number v′ of H+2(v′) varies with the increment of the projectile energy; and the electronic and vibrational state-selective differential cross sections show similar behaviors: there is a highest platform within a very small scattering angle，beyond which the differential cross sections decrease as the scattering angle increases and lots of oscillating structures appear，where the scattering angle of the first structure decreases as E-1/2p with the increment of the projectile energy Ep; and the structure and amplitude of the differential cross sections are sensitive to the orientation of molecule H2，which provides a possibility to identify the orientations of molecule H2 by the vibrational state-selective differential scattering processes.

Ab initioinvestigation of electron capture byCl7+ions from H

An investigation of charge transfer in collisions of ground-state ${\text{Cl}}^{7+}$ with H has been conducted based on a fully quantum-mechanical molecular-orbital close-coupling (QMOCC) approach. The charge-transfer process ${\text{Cl}}^{7+}(^{1}S)+\text{H}\ensuremath{\rightarrow}{\text{Cl}}^{6+}(2{p}^{6}n\ensuremath{\ell}\text{ }^{2}S,{^{2}P}^{o},^{2}D,{^{2}F}^{o},^{2}G)+{\text{H}}^{+}$ with $n=5$ and 6 is taken into account for collision energies between ${10}^{\ensuremath{-}4}\text{ }\text{eV}∕\text{u}$ and 1 keV/u. The relevant adiabatic potentials and nonadiabatic coupling matrix elements for the ${\text{ClH}}^{7+}$ system are evaluated with the configuration-interaction method. The investigation shows that electron capture into the $5d$, $5f$, $5g$, and $6p$ states dominates for collision energies less than $\ensuremath{\sim}1\text{ }\text{eV}∕\text{u}$, while above 100 eV/u the $5s$, $5p$, $5d$, and $6p$ are the primary capture channels. Comparison with experimental data for collisions of ${\text{Cl}}^{7+}(^{1}S)$ with D reveals a discrepancy over the full range of measured energies (5--430 eV/u), while no significant isotope effect is found for QMOCC calculations with deuterium. Furthermore, comparison with a previous calculation of the one-electron ${\text{N}}^{7+}+\text{H}$ system, as well as measurements of the multielectron ${\text{Al}}^{7+}+\text{H}$ and ${\text{Fe}}^{7+}+\text{H}$ systems, suggests that the electronic structure of the core has a non-negligible effect on the charge-transfer process. A one-electron model for relative $\ensuremath{\ell}$ distributions is found to agree with the QMOCC results for $n=5$ between 100 and 1000 eV/u, but fails at lower collision energies. Finally, state-selective and total rate coefficients are given for temperatures between 10 and 200 000 K.

Charge transfer and ionization in collisions ofSi3+with H from low to high energy

Charge transfer processes due to collisions of ground state ${\mathrm{Si}}^{3+}(3s\phantom{\rule{0.3em}{0ex}}^{1}S)$ ions with atomic hydrogen are investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) and classical-trajectory Monte Carlo (CTMC) methods. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained from Herrero et al. [J. Phys. B 29, 5583 (1996)] which were calculated with a full configuration-interaction method. Total and state-selective single-electron capture cross sections are obtained for collision energies from $0.01\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{u}$ to $1\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\mathrm{u}$. Total and state-selective rate coefficients are also presented for temperatures from $2\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ to ${10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Comparison with existing data reveals that the total CTMC cross sections are in good agreement with the experimental measurements at the higher considered energies and that previous Landau-Zener calculations underestimate the total rate coefficients by a factor of up to two. The CTMC calculations of target ionization are presented for high energies.

Electron capture in collisions of S withH+

Within the framework of a fully quantum-mechanical molecular-orbital close-coupling (QMOCC) theory, charge transfer has been studied for collisions of S with ${\mathrm{H}}^{+}$. The multireference single- and double-excitation configuration-interaction method was utilized to evaluate the adiabatic potentials and nonadiabatic coupling matrix elements for the $S{\mathrm{H}}^{+}$ system. Cross sections and rate coefficients are presented for $S(^{3}P,^{1}D)+{\mathrm{H}}^{+}\ensuremath{\rightarrow}{S}^{+}(^{4}S^{0},^{2}D^{0},^{2}P^{0})+\mathrm{H}$ with relative collision energies between $0.1\phantom{\rule{0.3em}{0ex}}\mathrm{meV}∕u$ and $10\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕u$ and temperatures between $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $2.0\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The investigation shows that the charge-transfer process is dominated by $S(^{3}P)+{\mathrm{H}}^{+}\ensuremath{\rightarrow}{S}^{+}(^{2}P^{0})+\mathrm{H}$ and that the cross sections and rate coefficients vary by orders of magnitude over the energy and temperature range considered. The current rate coefficients are in disagreement with the often adopted value of $1.30\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s}$ at low temperatures, and two orders of magnitude smaller than a previous estimate at $T={10}^{4}\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, for the process $S(^{3}P)+{\mathrm{H}}^{+}\ensuremath{\rightarrow}{S}^{+}(^{2}D^{0},^{2}P^{0})+\mathrm{H}$. We also perfomed semiclassical close-coupling calculations, which give cross sections in excellent agreement agreement with the QMOCC results for energies above $30\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕u$. Application of the results to astrophysical environments is briefly discussed.

Electron capture in collisions ofN+with H andH+with N

Charge-transfer processes due to collisions of N{sup +} with atomic hydrogen and H{sup +} with atomic nitrogen are investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) method. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial and rotational couplings obtained with the multireference single- and double-excitation configuration interaction approach. Total and state-selective cross sections for the energy range 0.1 meV/u-1 keV/u are presented and compared with existing experimental and theoretical data. A large number of low-energy resonances are obtained for exoergic channels and near thresholds of endoergic channels. Rate coefficients are also obtained and comparison to previous calculations suggests nonadiabatic effects dominate for temperatures greater than 20 000 K, but that the spin-orbit interaction plays a major role for lower temperatures.

Ab initiostudy of charge transfer inB2+low-energy collisions with atomic hydrogen

Charge transfer processes due to collisions of ground state B{sup 2+}(2s {sup 2}S) ions with atomic hydrogen are investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) method. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial and rotational coupling matrix elements obtained with the spin-coupled valence-bond approach. Total and state-selective cross sections and rate coefficients are presented. Comparison with the existing experiments shows our results to be in good agreement. When E 400 eV/u, inclusion of rotational coupling increases the total cross section by 50%-80%, improving the agreement between the current calculations and experiments. For state-selective cross sections, rotational coupling induces mixing between different symmetries; however, its effect, especially at low collision energies, is not as important as had been suggested in previous work.

Charge transfer ofO3+ions with atomic hydrogen

Charge transfer processes due to collisions of ground state ${\mathrm{O}}^{3+}{(2s}^{2}2p{}^{2}P)$ ions with atomic hydrogen are investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) method. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial and rotational coupling matrix elements obtained with the spin-coupled valence-bond approach. Total and state-selective cross sections and rate coefficients are presented. Comparison with existing experimental and theoretical data shows our results to be in better agreement with the measurements than the previous calculations, although problems with some of the state-selective measurements are noted. Our calculations demonstrate that rotational coupling is not important for the total cross section, but for state-selective cross sections, its relevance increases with energy. For the ratios of triplet to singlet cross sections, significant departures from a statistical value are found, generally in harmony with experiment.

Low-Energy Charge Transfer in Multiply-Charged Ion-Atom Collisions Studied with the Combined SCVB-MOCC Approach

A survey of theoretical studies of charge transfer involving collisions of multiply-charged ions with atomic neutrals (H and He) is presented. The calculations utilized the quantum-mechanical molecular-orbital close-coupling (MOCC) approach where the requisite potential curves and coupling matrix elements have been obtained with the spin-coupled valence bond (SCVB) method. Comparison is made among various collision partners, for equicharged systems, where it is illustrated that even for total charge transfer cross sections, scaling-laws do not exist for low-energy collisions (i.e. < 1 keV/amu). While various empirical scaling-laws are well known in the intermediateand high-energy regimes, the multi-electron configurations of the projectile ions results in a rich and varied low-energy dependence, requiring an explicit calculation for each collision-partner pair. Future charge transfer problems to be addressed with the combined SCVB-MOCC approach are briefly discussed.