K x rays produced in collisions of bare ions with atoms: Contribution of multiple-electron transfer in Kr³⁶⁺, Ar¹⁸⁺, and Ne¹⁰⁺+Ar collisions

K x rays have been observed in low energy collisions of bare Kr, Ar, and Ne ions with a neutral gas target. Although largely neglected previously, we have found that multiple-electron transfer processes play a significant role in shaping the x-ray spectra. The observed ratios of normal-satellite to hyper-satellite line intensities are found to be roughly independent of the ion species and much larger than those estimated from previously reported electron transfer cross sections, suggesting that there may be a strong correlation between two electrons during the electron transfer or during the subsequent cascades. It is suggested that exact knowledge of the initial and final principal and angular momentum quantum numbers (n,l) in electron transfer are the most essential missing ingredients for understanding the entire x-ray emission process in astrophysical, laboratory, and technological plasmas