Electron–He+2 scattering calculation using the R-matrix method: resonant and bound states of He2

The UK molecular R-matrix codes are used to study electron collisions with the He+2 molecular ion. Full configuration interaction calculations are performed to obtain the potential energy curves of the ground X 2Σ+u and the first excited 2Σ+g electronic states of He+2. Resonances, effective quantum numbers, and resonance widths as a function of the internuclear separation are determined for the lowest singlet 1Σ+g, 1Σ+u, 1Πg and 1Πu and triplet 3Σ+g, 3Σ+u, 3Πg, 3Πu and 3Δu states, which are relevant for the study of the reactive collision of He+2 with low-energy electrons. In addition, bound states are also calculated for each symmetry of He2 at several geometries

Dissociative recombination and rotational transitions of D2+_2^+ in collisions with slow electrons

Rate coefficients for dissociative recombination and state-to-state rotational transitions of the D$_{2}^{+}$ ion induced by collisions with very low-energy electrons have been reported following our previous studies on HD$^{+}$ and H$_{2}^{+}$ [9,10]. The same molecular structure data sets, excitations ($N_{i}^{+} \rightarrow$ $N_{f}^{+}=N_{i}^{+}+2$ for $N_{i}^{+}=0$ to $10$) and de-excitations ($N_{i}^{+}$ $\rightarrow$ $N_{f}^{+}=N_{i}^{+}-2$, for $N_{i}^{+}=2$ to $10$) were used for collision energies ranging from $0.01$ meV to $0.3$ eV. Isotopic effects for dissociative recombination and rotational transitions of the vibrationally relaxed targets are presented.Comment: 7 pages, 7 figures, 4 table

Assignment of resonances in dissociative recombination of HD+ ions: high-resolution measurements compared with accurate computations

The collision-energy resolved rate coefficient for dissociative recombination of HD+ ions in the vibrational ground state is measured using the photocathode electron target at the heavy-ion storage ring TSR. Rydberg resonances associated with ro-vibrational excitation of the HD+ core are scanned as a function of the electron collision energy with an instrumental broadening below 1 meV in the low-energy limit. The measurement is compared to calculations using multichannel quantum defect theory, accounting for rotational structure and interactions and considering the six lowest rotational energy levels as initial ionic states. Using thermal equilibrium level populations at 300 K to approximate the experimental conditions, close correspondence between calculated and measured structures is found up to the first vibrational excitation threshold of the cations near 0.24 eV. Detailed assignments, including naturally broadened and overlapping Rydberg resonances, are performed for all structures up to 0.024 eV. Resonances from purely rotational excitation of the ion core are found to have similar strengths as those involving vibrational excitation. A dominant low-energy resonance is assigned to contributions from excited rotational states only. The results indicate strong modifications in the energy dependence of the dissociative recombination rate coefficient through the rotational excitation of the parent ions, and underline the need for studies with rotationally cold species to obtain results reflecting low-temperature ionized media.Comment: 15 pages, 10 figures. Paper to appear in Phys. Rev. A (version as accepted

QDB: A new database of plasma chemistries and reactions

One of the most challenging and recurring problems when modeling plasmas is the lack of data on the key atomic and molecular reactions that drive plasma processes. Even when there are data for some reactions, complete and validated datasets of chemistries are rarely available. This hinders research on plasma processes and curbs development of industrial applications. The QDB project aims to address this problem by providing a platform for provision, exchange, and validation of chemistry datasets. A new data model developed for QDB is presented. QDB collates published data on both electron scattering and heavy-particle reactions. These data are formed into reaction sets, which are then validated against experimental data where possible. This process produces both complete chemistry sets and identifies key reactions that are currently unreported in the literature. Gaps in the datasets can be filled using established theoretical methods. Initial validated chemistry sets for SF 6 /CF 4 /O 2 and SF 6 /CF 4 /N 2 /H 2 are presented as examples

Electron–electron interaction effects in heliumlike atoms confined in finite external square-well potential

A B-spline-based configuration interaction method is used to compute the energy levels of the ground and a few excited states of heliumlike atoms confined in a finite external square-well potential, as a function of the depth of the confining shell potential. The electron probability density and the dependence of the energy levels in the shell potential are used to account for the electron-electron interaction when the atoms are submitted to such an environment

Stark broadening of the lower Rydberg

This paper deals with the calculation of line widths and lineshapes of the lower Rydberg lines of atomic hydrogen ($n\sim 5-20$) in the conditions of stellar envelopes and atmospheres - electron densities scaling from 109 to 1016 cm-3 and temperatures varying between 5000 and 40000 K. For these lines, the traditional semi-classical method breaks down, especially at low densities. Another or other theoretical approaches are needed for the determination of linewidths. An alternative tool is proposed in terms of collision rate methods. Data are provided for $n_\alpha$, $n_\beta$ and $n_\gamma$ lines