SLOW COLLISIONS OF O 6 + WITH He AND H 2 STUDIED IN ULTRA-SOFT X-RAY EMISSION

Photon emission in the 100-200A region following slow 06+ + He, H2 collisions has been analyzed using a new grazing incidence spectrometer. The ions were produced in an ECR type ion source, accelerated to 60 keV, and passed through a target gas cell. Intensity from decay associated with single electron transfer to nl levels is seen, and is used to deduce the relative nl subshell sefective capture cross sections. Many lines corresponding to double electron transfer are detected, and discussed in terms of different transfer mechanisms. Several lines are interpreted as due to correlated double capture. We also attribute intensity to the decay of quartet states, formed on metastable ls2s 3~ oxygen ion states by one-electron capture. About half of the quartet lines give evidence of non-core-conserving electron transfer. 1, Introduction Information on electron transfer processes in collisions of slow multicharged ions with atoms is'of great interest to many areas of research. The large cross sections for population of excited ionic states that have been observed underlie some of the importance of these phenomena in astrophysics, fusion research and plasma physics in general. Early evidence for population of excited states originating from electron capture during collisions between atoms and highly charged ions was given by soft x-ray emission from a tokamak plasma 11,21. Emission lines from oq+ (q=4,5,6,7) states, formed in collisions with hydrogen atoms, were identified. At about the same time, UV and VUV photon emission spectra from slow collisions were recorded 131, using an ion beam extracted from a Penning type ion source. Development of the ECR ion source 141 opened up the possibility to study slow charge transfer processes involving multicharged ions in more detail, and photon spectroscopic techniques from the UV to the ultra-soft x-ray (USX) region 15,61 has been applied to the excited projectile states populated in the collisions. The aim of the present paper is to report on photon emission in the 100-200A region subsequent to 60 keV 06+ + He, H2 collisions. The spectra enable us to derive the relative subshell selective single electron transfer cross sections, which we compare with previous experimental results and calculations. For the first time in the present wavelength region lines corresponding to correlated double electron transfer are identified. We also present observations implying non-core conserving single electron capture. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989135 C1-32% JOURNAL DE PHYSIQUE ULTRA-SOFT X-RAY EMISSION FOLLOWlNG CHARGE TRANSFER COLLISIONS