Impact-parameter dependence of K-shell excitation in slow ion-atom collisions

Beams of N, O, Ne, Na and Mg ions with an energy of a few hundred keV were injected into gaseous N 2 , O 2 , H 2 O and Ne targets under single-collision conditions. The experiment allowed simultaneous measurement of X-rays and Auger electrons in coincidence with ions scattered through angles from 0.9 to 40 degrees in the laboratory frame. The impact-parameter dependence of K excitation was found to show characteristic deviations from the predictions of the 2p sigma -2p pi rotational coupling theory. In the Ne-O collision system, the O K fluorescence yield exhibits a pronounced impact-parameter dependence. The dependence of the total fluorescence yield omega K on ion energy and charge state has been measured.