A large-scale R-matrix calculation for electron-impact excitation of the Ne2 +, O-like ion

Abstract

The five JΠ 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. Previous R-matrix calculations for the O-like Ne ion, Ne2 +, exhibit spurious structure in the cross sections at higher electron energies, which may affect Maxwellian averaged rates even at low temperatures. Furthermore, there is an absence of comprehensive excitation data between the excited states that may provide newer diagnostics to complement the more established lines discussed in this paper. To resolve these issues, we present both a small-scale 56-level Breit–Pauli calculation and a large-scale 554-level R-matrix intermediate coupling frame transformation calculation that extends the scope and validity of earlier JAJOM calculations both in terms of the atomic structure and scattering cross sections. Our results provide a comprehensive electron-impact excitation data set for all transitions to higher n-shells. The fundamental atomic data for this O-like ion are subsequently used within a collisional radiative framework to provide the intensity line ratios across a range of electron temperatures and densities of interest in astrophysical observations.