Electron collisions with Fe-peak elements: Fe IV

Abstract

Electron-impact excitation collision strengths of the Fe-peak element Fe IV are calculated in the close-coupling approximation using the parallel R -matrix program PRMAT. One hundred and eight LS – coupled states arising from the $\rm 3d^5$, $\rm 3d^44s$ and $\rm 3d^44p$ configurations of Fe IV, are retained in the present calculations. Accurate multi-configuration target wavefunctions are employed with the aid of $\rm 3p^2 \rightarrow 3d^2$ electron promotions and a $\overline{\rm 4d}$ correlation orbital. The effective collision strengths required in the analysis of astrophysically important lines in the Fe IV spectra, are obtained by averaging the electron collision strengths for a wide range of incident electron energies, over a Maxwellian distribution of velocities. Results are tabulated for forbidden transitions between the $\rm 3d^5$, $\rm 3d^44s$ and the $\rm 3d^44p$ manifolds for electron temperatures ( T e in degrees Kelvin) in the range $3.3 \leq {\rm Log} \, T_{\rm e} \leq 6.0$ that are applicable to many laboratory and astrophysical plasmas. The present results provide new results for forbidden lines in the Fe IV spectrum studied here.