Angular Distribution and Polarization of the 3C and 3D Lines Following Electron-impact Excitation of Fe16+ Ions

The electron-impact excitations from the ground state to the excited levels and as well as the subsequent radiative decays of neonlike Fe 16+ ions have been investigated within the framework of the multiconfigurational Dirac–Fock method and the relativistic distorted-wave theory. Special attention has been paid to emission behaviors of the astrophysically relevant resonance 3 C and intercombination 3 D lines emitted in the radiative decays of Fe 16+ ions. To this end, we calculate the angular distribution and linear polarization of both of the lines for a series of impact electron energies. It is found that the angular and polarization behaviors of the resonance 3 C line are nearly the same as those of the intercombination 3 D line. Nevertheless, the angular and polarization behaviors of both of the lines are found to be very sensitive to the impact electron energy, especially at low impact energies. Based on such a sensitivity, it is expected that high-precision angular and polarization measurements of the 3 C and 3 D lines could be served as a tool for revealing detailed information such as electron energy of relevant laboratory and astrophysical plasmas.