X-ray emission measurements following charge exchange between O$^{8+}$ and Kr

Lyman spectra and line-ratios for soft X-ray following charge exchange between O$^{8+}$ and Kr were measured using a beam-gas technique and a high resolution microcalorimeter X-ray detector for the collision velocities from 293 km/s to 1256 km/s. Ly-$\alpha$, Ly-$\beta$, Ly-$\gamma$, Ly-$\delta$, Ly-$\varepsilon$ lines of O$^{7+}$ ion were identified, as well as minor transition lines from O$^{6+}$. Our observed line ratios are compared to a single charge exchange model, specifically with theoretical calculations for O$^{8+}$ - H. Good agreement is found for the line ratio from the dominant $n = 5$ capture states, with direct capture and cascade having an important influence on the line ratio for the $n = 4$ states. Moreover, for velocities lower than 600 km$/$s, X-ray emission following autoionizing double capture results in Ly-$\alpha$ and Ly-$\beta$ enhancement, the former leads to the Ly-$\varepsilon$/Ly-$\alpha$ line ratios significantly smaller than theoretical calculations, the latter leads to the Ly-$\beta$/Ly-$\alpha$ line ratios larger than theory. The apparatus is being modified to perform measurements with H using a merged-beam technique.