Electron-Impact Excitation of Ne II (original) (raw)
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A large-scale R-matrix calculation for electron-impact excitation of the Ne2+, O-like ion
2011
Abstract The five J levels within an np2 or np4 ground-state complex provide an excellent testing ground for the comparison of theoretical line ratios with astrophysically observed values, in addition to providing valuable electron temperature and density diagnostics. The low-temperature nature of the line ratios ensures that the theoretically derived values are sensitive to the underlying atomic structure and electron-impact excitation rates.
Physical Review A, 2002
Electron-impact differential cross-section measurements for the excitation of the 2p 5 3s configuration of Ne are reported. The Ne cross sections are obtained using experimental differential cross sections for the electronimpact excitation of the nϭ2 levels of atomic hydrogen ͓Khakoo et al., Phys. Rev. A 61, 012701-1 ͑1999͔͒, and existing experimental helium differential cross-section measurements, as calibration standards. These calibration measurements were made using the method of gas mixtures ͑Ne and H followed by Ne and He͒, in which the gas beam profiles of the mixed gases are found to be the same within our experimental errors. We also present results from calculations of these differential cross sections using the R-matrix and unitarized first-order many-body theory, the distorted-wave Born approximation, and relativistic distorted-wave methods. Comparison with available experimental differential cross sections and differential cross-section ratios is also presented.
Effective Collision Strengths for Electron Impact Excitation of N I
Atomic Data and Nuclear Data Tables, 2000
Electron collision strengths for electron-impact excitation of the Li-like Al ion are evaluated in the close-coupling approximation using the multichannel R-matrix method. Five LS target eigenstates are included in the expansion of the total wave function, consisting of the two n =2 states with configurations 1s 2 2s, 1s 2 2p, and the three n =3 states with configurations 1s 2 3s, 1s 2 3p, 1s 2 3d. These five ionic states correspond to eight fine-structure levels leading to a total of 18 independent transitions. The collision strengths for all possible allowed transitions are tabulated for electron energies in the range of 0.19 -0.3 Ry, which are the temperatures of interest for many plasma applications.
Collision strengths for the electron impact of the fine-structure levels within the ground term of Ne + and Ne 2 + are calculated using the Breit–Pauli R-matrix and the Dirac atomic R-matrix code (DARC) methods. Maxwellian-averaged effective collision strengths are presented for each ion. The application of the current calculations is to very low temperature astrophysical plasmas, down to 10 K, and thus we examine the sensitivity of the effective collision strengths to the resonance positions and underlying atomic structure. The use of the various theoretical methods allows us to place estimated uncertainties on the recommended effective collision strengths. Good agreement is found with previous R-matrix calculations at higher temperatures.
Electron-impact study of NeF using the R-matrix method
Physical Review A, 2008
Noble gas-halogen complexes form the basis of possible excimer lasers. Electron collisions are investigated with the prototypical neon fluoride molecule as a function of internuclear separation. The study concentrates on the four states making up the excimer system: The low-lying X 2 ⌺ + and A 2 ⌸ repulsive states and the highlying 1 2 ⌺ + and 2 2 ⌸ charge-transfer states which can support bound states. These states are represented using a configuration-interaction expansion which is shown to yield accurate potential energy curves and target properties. Elastic and inelastic collision cross sections for the four states are calculated ab initio using the R-matrix method. Special care is needed to treat the large dipole moments found for the charge-transfer states which are predicted to have electron collision cross sections almost two orders of magnitude bigger than the lower states. Differential and momentum transfer cross sections are also considered for the electron impact on the repulsive ground state. Rate constants for electron deexcitation of the excimer states of NeF have been calculated for electron temperature corresponding up to 10 eV. The superelastic processes are dominated by the 1 2 ⌺ + → X 2 ⌺ + transition with thermal rate constant of ͑2-5͒ ϫ 10 −9 cm 3 s −1 in the entire range of electron temperature considered.
Journal of Physics B, 2017
There are major discrepancies between recent ICFT (Intermediate Coupling Frame Transformation) and DARC (Dirac Atomic R-matrix Code) calculations (Fernández-Menchero et al. 2014, Astron. Astroph. 566 A104, Aggarwal et al. 2016 Mon. Not. R. Astr. Soc. 461 3997) regarding electron-impact excitation rates for transitions in several Be-like ions, as well as claims that the DARC calculations are much more accurate and the ICFT results might even be wrong. To identify possible reasons for these discrepancies and to estimate the accuracy of the various results, we carried out independent B-Spline R-Matrix (BSR) calculations for electron-impact excitation of the Be-like ion N 3+. Our close-coupling expansions contain the same target states (238 levels overall) as the previous ICFT and DARC calculations, but the representation of the target wave functions is completely different. We find close agreement among all calculations for the strong transitions between low-lying states, whereas there remain serious discrepancies for the weak transitions as well as for transitions to highly excited states. The differences in the final results for the collision strengths are mainly due to differences in the structure description, specifically the inclusion of correlation effects, rather than the treatment of relativistic effects or problems with the validity of the three methods to describe the collision. Hence there is no indication that one approach is superior to another, until the convergence of both the target configuration and the close-coupling expansions have been fully established.
A full CI treatment of Ne atom - a benchmark calculation performed on the NAS CRAY 2
Chemical Physics Letters, 1986
Full CI calculations are performed for Ne atom using Gaussian basis sets of up to triple-zeta plus double polarization quality. The total valence correlation energy through double, triple, quadruple and octuple excitations is compared for eight different basis sets. These results are expected to be an important benchmark for calibrating methods for estimating the importance of higher excitations.
Physical Review A, 2013
The electron-polarized-photon coincidence method is used to determine linear and circular polarization correlations in vacuum ultraviolet (VUV) for the differential electron-impact excitation of neon and argon resonance transitions at impact energies of 25 and 30 eV at small scattering angles up to 40 •. The circular polarization correlation is found to be positive in the case of Ne at 25 eV and supports the prediction of the present B-spline R-matrix theory concerning the violation of a long-established propensity rule regarding angular momentum transfer in electron-impact excitation of S → P transitions. Comparisons with the results from the present relativistic distorted-wave approximation and an earlier semirelativistic distorted-wave Born model are also made. For the case of Ar, at 25 and 30 eV, the circular polarization measurements remain in agreement with theory, but provide limited evidence as to whether or not the circular polarization at small scattering angles is also positive. For the linear polarizations, much better agreement with theory is obtained than in earlier measurements carried out by S. H. Zheng and K. Becker [Z.