Excitation Cross Sections For Electron Collisions Research Articles

Quantum Geometry: Generalized version of an energy approach in scattering theory and its application to electron-collisional excitation of multicharged ions

Within quantum geometry it is presented the Generalized version of the energy approach in scattering theory and its application to electron-collisional excitation of multicharged ions. The reestimated numerical data for electron-collisional excitation cross-sections are presented for barium.

Квантовая геометрия: Применение обобщенного энергетического подхода в теории рассеяния для многозарядных ионов

Within quantum geometry it is presented an advanced energy approach in scattering theory and its application to calculation of cross-sections of elementary processes for complex atomic systems. The improved numerical data for electron-collisional excitation cross-sections are presented for barium.

Bound and continuum states of molecular anions C2H− and C3N−

Recently a number of molecular anions, closed-shell linear carbon chains of the form CnH− and CnN−, have been detected in space. The molecules C2H− and C3N− are investigated by using the R-matrix method to consider electron scattering from the corresponding neutral targets. Initial target calculations are conducted and refined in order to produce target state characteristics similar to the experimental data. A number of different scattering models are tested including static exchange and close-coupling models, and the use of Hartree–Fock or natural orbitals in the close-coupling calculations. The calculations concentrate on bound and resonances states for the anions as well as eigenphase sums, elastic cross-sections and electronic excitation cross-sections for electron collisions with the neutral. It is found that electronic resonances are all too high in energy to be important for anion formation in the interstellar medium. However, C3N−, unlike C2H−, supports a number of very weakly bound excited states, which may well provide the route to electron attachment for this system.

Diagnostics of the collisionally pumped plasma and search of the optimal plasma parameters of x-ray lasing: calculation of electron-collision strengths and rate coefficients for Ne-like plasma

The problem of diagnostics for the collisionally pumped plasma and search of the optimal plasma parameters of x-ray lasing are studied. We present the uniform energy approach, formally based on the quantum electrodynamics with using gauge invariant scheme of generation of the optimal one-electron representation, for the calculation of electron collision strengths and rate coefficients for electron-collisional excitation. The aim is to study, in a uniform manner, elementary processes responsible for emission-line formation in plasmas. The electron collision excitation cross-sections and rate coefficients for some Ne-like ions (Fe, Ba) are calculated. To test the results of calculations we compare them with other authors calculations and with available experimental data.

Accurate cross sections for excitation of resonance transitions in atomic oxygen

Electron collision excitation cross sections for the resonance 2p43P–2p33s3So, 2p43P–2p33d3Do, 2p43P–2p33s3Do, 2p43P–2p33s3Po, and 2p43P–2s2p53Po transitions have been calculated by using the R matrix with a pseudostates approach for incident electron energies from near threshold to 100 eV. The excitation of these transitions gives rise to strong atomic oxygen emission features at 1304, 1027, 989, 878, and 792 Å in the spectra of several planetary atmospheres. We included 22 spectroscopic bound and autoionizing states and 30 pseudostates in the close‐coupling expansion. The target wave functions are chosen to properly account for the important correlation and relaxation effects. The effect of coupling to the continuum is included through the use of pseudostates. The contribution of the ionization continuum is significant for resonance transitions. Measured absolute direct excitation cross sections of O I are reported by experimental groups from the Jet Propulsion Laboratory and Johns Hopkins University. Good agreement is noted for the 2p43P–2p33s3So transition (λ1304 Å) with measured cross sections from both groups that agree well with each other. There is disagreement between experiments for other transitions. Our results support the measured cross sections from the Johns Hopkins University for the 2p43P–2p33d3Do and 2p43P–2p33s3Do transitions, while for the 2p43P–2p33s3Po transition the agreement is switched to the measured cross sections from the Jet Propulsion Laboratory.

Oscillator strengths and inelastic scattering of electrons from O II

Electron-collision excitation cross sections of inelastic transitions among the 28 LS terms of the 2s22p3, 2s2p4, 2s22p23s, 2s22p23p, 2s22p23d and 2s22p24s configurations of singly-ionized oxygen are calculated using the R-matrix method. The target states are represented by fairly extensive configuration-interaction wavefunctions which yield excitation energies, oscillator strengths and radiative lifetimes of excited states that agree well with available calculated and measured values. To assess the importance of electron correlation and coupling to higher excited states in the scattering calculation, the present 28-state calculation is compared with the earlier 11-state R-matrix theory. Our cross sections for the 2s22p3 4So-2s22p3 2Do and 2s22p3 4So-2s2p4 4P transitions show good agreement with the merged-beams energy-loss experiment and the 11-state R-matrix theory.

Status of the multiply-charged ion research facility at JPL

A new research facility for the study of interactions of multiply-charged ions has recently been completed at the Jet Propulsion Laboratory. A 1.2 tesla/14.0 GHz Caprice-type electron-cyclotron-resonance (ECR) ion source is used to produce highly-charged ions. The JPL facility can deliver ions into three experimental stations. Two are currently in operation for (a) measurement of absolute electron collisional excitation cross sections, and (b) measurement of lifetimes and f-values of metastable levels.

The influence of metastables on the plasma-induced emission in a helium rf discharge

Space- and time-resolved emission spectroscopy is commonly used to investigate heating mechanisms in rf discharges (plane parallel plate configuration). The metastable density in these discharges is several orders of magnitude lower than the density of the ground-state atoms; however, the electron collision excitation cross sections of some helium levels out of the metastable levels exhibit values which are several orders of magnitude larger and have much lower thresholds than those for the ground state. It is therefore questionable whether stepwise excitation from metastable levels can be neglected in the interpretation of the spatiotemporal plasma-induced emission of rf discharges. To our knowledge only the excitation of ground-state atoms has been taken into account in model calculations to this date. With respect to the energy balance of such a discharge, this assumption is probably correct. However, with respect to the emission of light, our computational results show that some specific levels are excited significantly by electron collisions with metastables. We will show in this contribution, on the basis of our measurements, that this effect is responsible for the observed emission profiles of some lines. Consequently, the interpretation of the emission profiles in helium rf discharges has to take account of the role of metastables.

Excitation-autoionization processes in electron-impact ionization of Au68+

Relativistic electron-impact ionization cross sections have been calculated for Au{sup 68+}. Direct ionization cross sections were computed using a relativistic distorted-wave method. Relativistic distorted-wave electron collisional excitation cross sections and detailed relativistic radiative and Auger rates were calculated in order to determine the contribution of excitation-autoionization processes. Because radiative channels are the predominant decay modes for highly charged heavy ions, the effects of excitation-autoionization processes were expected to be small for Au{sup 68+}. However, we found that these processes enhance the direct ionization cross sections by a factor of 4. This enhancement may be observed in experiments on the electron-beam ion trap in the near future.

Oscillator strengths and electron collisional excitation cross sections for atomic oxygen.

Absorption oscillator strengths for dipole-allowed transitions among the 2${p}^{4}$ $^{3}P$, 3s $^{5}$,3S\ifmmode^\circ\else\textdegree\fi{}, 3p $^{5}$,3P, 4s $^{5}$,3S\ifmmode^\circ\else\textdegree\fi{}, 3d $^{5}$,3D\ifmmode^\circ\else\textdegree\fi{}, 4p $^{5}$,3P, and 3s' $^{3}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$ states of O i are calculated in length and velocity formulations using extensive configuration-interaction wave functions. We also include these 12 states in our close-coupling calculations of the inelastic cross sections for O i. Cross sections for excitation of the 3s $^{5}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$, 3p $^{5}P$, 4s $^{3}S$\ifmmode^\circ\else\textdegree\fi{}, 4p $^{3}\mathrm{P}$, 3d $^{3}D$\ifmmode^\circ\else\textdegree\fi{}, and 3s' $^{3}D$\ifmmode^\circ\else\textdegree\fi{} states by electron impact are presented in the energy region from 13.87 to 100 eV and these are compared, where available, with other calculations and experiments. The present results are in good agreement with the recent experiments at energies 13.87, 20, and 30 eV for the $^{3}\mathrm{p}$ $^{5}\mathrm{P}$ transition and at energies 13.87 and 16.5 eV for the $^{3}\mathrm{s}$ $^{5}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$ transition. However, the present cross sections for the $^{3}\mathrm{s}$ $^{5}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$ transition at 20 and 30 eV are large by a factor of 2 compared to experiment. There are discrepancies between theory and experiment in magnitude for the dipole-allowed $^{3}\mathrm{d}$ $^{3}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$ and $^{3}\mathcal{'}$ $^{3}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$ transitions.

Electron collisional excitation cross sections for Fe III and Fe VI and iron abundances in gaseous nebulae

We have calculated electron impact excitation cross sections between most of the low metastable levels of Fe III and Fe VI, using the close-coupling method. In addition, we have recalculated the electric quadrupole and magnetic dipole transition probabilities for these transitions in Fe VI. The statistical-equilibrium equations appropriate to a collisional/radiative model are solved to obtain level populations for each ion. Line emissivities have been calculated for the forbidden lines (Fe III) and (Fe VI). Comparison is made with with intensities in several nebulae and peculiar stars. The iron abundances in the Orion Nebula, NGC 6720, NGC 7009, and NGC 7662 are discussed. NGC 7662 seems to have an iron abundance an order of magnitude smaller than the sular abundance.

Utility of Gaussian-Type Orbitals in Molecular Collisions: Electronic Excitation of the First Positive System of the Nitrogen Molecule

The use of gaussian-type orbitals (GTO) as basis sets of electronic wave functions of molecules for calculating electron-collision excitation cross sections is discussed. A test calculation of the electron excitation cross section of the 2p state of atomic hydrogen at 60-1000 eV in which the hydrogenic wave functions were expressed as linear combinations of GTO indicates that an expansion of the is wave function by six GTO's and the 2p by four GTO's gives quite accurate results. Methods for evaluating the multicenter integrals which appear in the expressions of electron-excitation cross section (by the Born-type approximation) of diatomic molecules are described. Cross sections of direct electron excitation of the B(3)II(g) state (the first positive bands) of the N(2) molecule are calculated by this scheme, and the results are in good agreement with experiments.

Electron excitation and emission of the resonance lines of Si II

Electron collisional excitation cross sections of all allowed resonance transitions in Si II have been calculated using semi-classical perturbation theory. Allowance has been made for violation of the unitary condition on the S matrix due to coupling between all resonance states and the ground state. These cross sections were used to calculate the relative intensities of allowed and forbidden ultra-violet resonance lines of Si II emitted both by the sun and ZETA. The allowed line intensities are very sensitive functions of electron temperature while the forbidden lines are sensitive monitors of the electron density. Comparison with observation suggests the (rate averaged) cross sections are accurate to within a factor of two.