Analysis of radiative emissions in O$^{6+}$-argon, -water, and -methane charge-exchange collisions

Charge exchange between highly-charged (solar wind) ions and neutrals is the main mechanism responsible for the observed x-ray emission from comets. A recent joint experimental/theoretical work looked at these processes for O$^{6+}$ collisions with argon atoms and a variety of molecules including water and methane at impact energies which correspond to the low and high solar wind speeds [1]. In the present work we study these collision systems using the two-center basis generator method within the independent electron model [2]. For the molecular targets we used a spectral representation of the target Hamiltonian and found that a closure approximation was necessary to produce reliable total cross section results for single-, double-, and triple-electron transfer. For the single-electron transfer channel we carried out a radiative cascade analysis and compared the resulting emission spectra with the classical-trajectory Monte Carlo calculations reported in [1]. Overall, the agreement is satisfactory. [1] J. R. Machacek \textit{et al}., Astrophys. J. \textbf{809} 75 (2015). [2] A. C. K. Leung and T. Kirchner, Phys. Rev. A \textbf{95} 042703 (2017).