| The discovery of cometary X-ray emission for the first time in 1996, from comet Hyukatake using the Rontgen satellite (ROSAT) [Lisse, C. M. et al., 1996] was a highly surprising event. Since then, X-ray and extreme ultra violet (X-EUV) emission has been observed from a number of comets [Lisse, C. M. et al., 2001]. The production of such radiation is strongly believed to be the result of the charge exchange collisions of the minor heavy highly charged solar wind (SW) ions with cometary neutrals. This study reports the first state-selective He-like X-ray spectra resulting from single-electron capture (SEC) in charge exchange collisions of O7+ and Ne 9+ with He and CO targets at a collision velocity of 800 km/s. The ions and velocity are typical of solar wind ions while the molecular and atomic targets are typical of cometary (CO) and interstellar (He) neutrals. The spectra have been obtained by means of simultaneous cold-target recoil ion momentum spectroscopic (COLTRIMS) and X-ray spectroscopic measurements that involved the triple-coincident detection of X-rays, scattered projectile, and target recoil ions. The spectra test the ability of theories to account for the relative population of triplet and singlet states in He-like product ions following SEC. The O7++He spectra are compared with theoretical spectra based on quantal molecular-orbital close-coupling (QMOCC) and multi-channel Landau-Zener (MCLZ) calculations. In addition, all spectra have been used to extract angular momentum distributions based on the traditional 3:1 triplet-to-singlet ratio assumption for the populated states. The QMOCC and MCLZ calculations and the experimental results, however, suggest significant departures from this assumption. The extracted l-distributions are state-of-the-art at this time for modeling purposes due to the high differentiation power of the experimental procedure. |
