Common Translation Factor Research Articles

Electron capture and excitation processes in theLi(2s; 2pσ, 2pπ)+H+ collision(0.1-10 keV)

Li(n = 2) to H*(n = 2,3) and Li*(2p, n = 3) charge transferand excitation processes are studied in the medium-energy range0.1-10 keV. The static model includes a basis of 26 molecularstates. The lithium atom is described using a model potentialand the semiclassical impact parameter method with straighttrajectories is used for the dynamical simulation. A commontranslation factor is included to account correctly for theelectron translation movement.For this collision system, we calculate the total cross sectionsand probabilities for the different capture and excitationprocesses. The calculation reflects a Lyα radiationenhancement for the capture to H*(2p) from Li*(2p). Astrong alignment effect in the capture processes to H*(2)is also shown and evaluated through the alignment parameterA(n = 2,3). Finally, we provide a mechanism through thenon-adiabatic radial and rotational couplings, showing theimportance of the H*(3) and Li*(3) states in thiscollision.

Quantal and semiclassical calculations of charge transfer cross sections in + H collisions for impact energies of

Total and n-partial cross sections for charge transfer in collisions are calculated for collision energies between and . A molecular expansion is employed, and semiclassical and quantal calculations are carried out including a common translation factor and a common reaction coordinate, respectively. The comparison between quantal and semiclassical cross sections and transition probabilities is discussed.

Electron transfer in keV collisions: II. Molecular basis model

The velocity dependence of state-to-state integral cross sections for electron transfer and excitation in collisions is studied in the 0.05 - 0.3 au velocity range using the impact parameter semi-classical method and a 28-state molecular orbital basis model including a common translation factor. The initial orbital alignment dependence of electron transfer is in fair agreement with recent experiments and with atomic orbital model calculations. The main electron transfer channel from is to the states. The integral cross sections from an aligned or oriented state to an aligned or oriented state and vice versa and the corresponding alignment and orientation parameters are presented as a function of the impact velocity.

Molecular treatment of H++He+(1s) collisions including pseudostates.

We report close-coupling calculations in a basis of molecular states, modified with a common translation factor, and augmented with a set of pseudostates, for ${\mathrm{H}}^{+}$ + ${\mathrm{He}}^{+}$ collisions for impact energies from 9 to 300 keV/amu.

Active Electrons in the CHe 4+ Quasimolecule

Low energy C4++ He collisions are known to be unusual in the sense that double-electron transfer dominates single capture. A basic question is whether one, two or more active electrons play a role in these processes. To study this problem, results are reported for the molecular energies and dynamical couplings of the CHe4+ system, modified with a common translation factor. The interactions that are responsible for the capture processes are discussed in detail, and as recently proposed in the literature, double capture is shown to occur simultaneously through essentially single-electron interactions. Some illustrative results of single- and double-charge exchange cross sections are also presented.

Charge transfer in slow N2++H collisions

We have performed quantal calculations of charge transfer in N2++H collisions in the range of centre of mass energies 0.1<E<100 eV amu-1. Molecular states were calculated using ab initio SCF-CI methods. Radial and angular couplings between the adiabatic molecular states were evaluated with allowance for a common translation factor. In agreement with earlier calculations, we find that charge transfer into the N+(2s2p33D0) share is dominant in the energy range considered and relevant to the study of photoionized nebulae. However, the cross sections and the rate coefficients that we have computed are smaller than the results of the earlier work by factors of about 1.5.

Alignment and orientation for charge exchange in Li+-Na(3s, 3p) collisions: II. Time-dependent outer electron density and current

The time evolving electronic density and current of the active outer electron in 1-2 keV Li+-Na(3p) collisions have been calculated and graphed. The corresponding time-dependent electronic wavefunction is provided by the 28 coupled molecular state calculations of the preceding paper with a common translation factor. The mechanism of the alignment effect for charge exchange from initially aligned Na(3p0 degrees /90 degrees ) or Na(3p45 degrees /-45 degrees ) is clearly seen in the graphs of the current.

Alignment and orientation for charge exchange in Li+-Na(3s, 3p) collisions: I. Differential and total cross sections

The alignment and orientation effects for charge exchange in 1-1.5 keV Li+-Na(3s, 3p) collisions are studied by semiclassical close-coupling calculations employing adiabatic molecular data and a common electron translation factor. The differential cross sections from Na(3s) to Li(2s) and Li(2p) are compared to experiment, a large orientation effect is predicted for charge exchange to Li(2p+or-1). From Na(3p) the charge exchange is important only to the Li(2p) channel, the corresponding alignment and orientation effects are calculated. The orientation effect follows the propensity rules. The formulae for total and differential cross sections for a transition from aligned p to p state or from oriented p to p state are derived. Two differential total cross sections for oriented p+or-1 to p+or-1 states can be defined, the same for aligned p+or-45 degrees to p+or-45 degrees states. The important role of the translation factor is discussed and a four state model is able to describe charge exchange from Na(3p) to Li(2p) at large impact parameters.

Common-translation-factor method with an atomic basis.

We show, for the benchmark case of ${\mathrm{He}}^{2+}$+H collisions, that a close-coupling expansion in terms of an atomic basis modified with a common translation factor is competitive with the molecular approach at low and intermediate impact energies.

Laser-enhanced Lyα emission from H +Li(2p m) collisions

Li(2s,2p)-H + charge transfer is studied using an eight adiabatic molecular basis and the impact parameter method with a common translation factor in the range 0.5–10 keV. The Lyα enhancement for capture to H(2p) from excited Li(2p) and orientation preference from Li (2p −1) is obtained.

Molecular data for the hydrogen quasimolecule using a one-electron model

We test the validity of one-electron models for homonuclear diatomic systems by a study of the molecular energies and dynamical couplings that are relevant in the treatment of H++H- collisions. We also present the modifications introduced in the couplings by a common translation factor that has proved suitable at high impact energies.

A three-state molecular model of electron capture from polarized Na*(3p) atoms

In the energy range of a few keV the orientation and alignment in electron capture by proton impact from polarized Na*(3p) atoms is studied in a semiclassical molecular model. The adiabatic basis functions, obtained using a model potential method, are modified by a common electron translation factor. The orientation effect is interpreted in terms of a three-state molecular model at large impact parameters 10 au(b(20 au even though the detailed study of the total cross sections requires at least 14 states of positive symmetry.

Alignment and orientation in Li(2pm)–H+charge-transfer collisions

Initial orbital alignment and orientation effects, have been studied in slow (0.2–10 keV) quasi-resonant charge-transfer collisions of laser-excited Li*(2p) atoms with H+ ions. The standard semi-classical impact parameter method with a common translation factor has been employed using an adiabatic molecular basis. Pronounced alignment effects for the transition to H*(n= 2) were found to be a function of collision energy but orientation preferences from Li*(2p–1) were obtained over the entire energy range.

Bonding in the (MgH) + quasimolecule

We have calculated the potentials for the MgH + quasimolecule, including seven 1,3Σ, three 1Π and four 3Π states. The calculations were carried out in the framework of full configuration interaction (CI) for the two valence electrons, the interaction of these electrons with the MgH 3+ core being described through a local Pseudopotential. We report also the radial and rotational couplings between these states using the CI wavefunctions modified with a common translation factor (CTF).

Charge exchange and excitation in C3++H collision. II. Partial and total cross section calculations

For pt.I see ibid., vol.24, no.18, p.4049-60 (1991). The authors report a treatment of slow C3++H collisions for impact energies E=0.04-9 keV amu-1, using an expansion in terms of 22 molecular states modified with a common translation factor. Calculated partial and total cross sections for charge exchange are in good agreement with measured ones. Cross sections and values for the alignment parameter for C3+ excitation are predicted. A detailed study of the collision dynamics is presented.

Electron capture in He2+-metastable H (2s) low energy collisions

The total and partial charge exchange cross sections for the collision He2+-H (2s) at impact velocities between 0.05 and 0.6 au are calculated. The transition amplitudes are obtained from the perturbed stationary states approximation corrected to account for the electron momentum transfer problem. It is shown that in the present case the results are very sensitive to the choice of the common translation factor (CTF) used to perform the calculations. Therefore, the authors use the Euclidean norm method in order to optimize the CTF. Finally, we study the effect of the Stark interaction before the collision on the process of capture.

Partial charge exchange and excitation cross sections for C3+ + H collisions

C3+ + H collisions are analyzed in the low-intermediate energy range where a Common Translation Factor (CTF) modified molecular approach is adequate. Following a previous conclusion [1] we present partial charge exchange (C.E.) and excitation cross sections for relevant channels.

Total and differential charge transfer cross sections in H++Na(3s) or Na*(3p) collisions

Proton-sodium charge transfer is studied, using 9- and 19-state adiabatic molecular bases and the impact parameter method, in the energy range 0.5-5 keV. The dynamical radial and rotational coupling terms and a common translation factor (CTF) are included. The effect of the choice of the coordinate centre on the total charge exchange cross sections to H(n=2) is clearly demonstrated when no CTF is included. The alignment dependence of the capture to H(n=2) is obtained and is satisfactorily compared with the atomic expansion calculations. State-to-state charge exchange differential cross sections are calculated; the alignment and orientation effects are expected to be observable at the collision energy 0.5 keV where they are spread out at scattering angles theta >0.1'.

AB initio studies of collisions between Na + ions

Self-consistent-field and configuration interaction procedures are used to calculate the potential energy curves and non-adiabatic couplings for the Na 2 2+ system. The lowest five 1Σ g six 1Π g and one 1Δ g states are included. The perturbed stationary state approach with a common translation factor is employed to study collisions between Na + ions for interaction energies between 5 and 80 keV. The calculated charge transfer cross section is in agreement with the observed cross section for Na 2+ formation at energy 20 keV. At higher energies, the calculated results fall steadily below the observations.

Alignment and spin exchange in the Na 3p excitation by He+-ion impact.

The 3s-3p excitation of Na atoms by ${\mathrm{He}}^{+}$ ions in the impact energy range 0.6--10 keV has been studied both experimentally and theoretically. In the experiment, the total excitation cross section, the alignment of the Na 3p state, and the collision-induced change of spin polarization of the Na valence electron were investigated. For the latter purpose, the Na atoms were polarized by a hexapole state selector, and a magnetic field was applied to the collision region, resulting in a spin polarization of the Na ground-state atoms of ${P}_{S}$\ensuremath{\approxeq}0.74. The spin polarization of the final 3p excited state was derived from the measured circular polarization of the fluorescence light. The experimental results are compared to published calculations in the Coulomb approach and to our own calculations in the molecular approach using a 12-state molecular expansion and employing a common translation factor. The molecular approach gives satisfying agreement with all experimental data. In particular, the measured increase of spin depolarization with decreasing collision energy is well reproduced. The depolarization originates from the exchange interaction between the 1s electron of ${\mathrm{He}}^{+}$ and the valence electron of Na during the collision.