Impact parameter dependence ofK-shell excitation probabilities in Ar ? Ar-collisions

Abstract

The impact parameter (b) dependence of theK-shell excitation probabilities (P K (b)) in the Ar on Ar collision system at 4.5, 8, 12 and 20 MeV impact energy have been measured over a wideb range (from the kinematik peak to far outside the adiabatic peak) for different projectile charge states. In agreement with the data of Lutz et al. and Nolte et al. a very strong increase ofP K (b) towards very smallb values (corresponding to scattering angles up to 40°) has been observed. From the measuredb and projectile charge state dependences it has been derived that for the systems investigated here the 2pπ-2pσ rotational coupling mechanism gives the dominant contribution to theK-shell excitation at very smallb (kinematic peak regime) as well as at very largeb (adiabatic peak regime). The analysis of the data indicates that in disagreement with the general assumption of ab independent 2pπ vacancy probability P2pπ , the probability P2pπ increases towards smallerb. At the high projectile energy the data confirm the results of Nolte et al. of a large dynamically produced probability P 2 and of strong contributions of direct 2pσ and 1sσ excitation to the measuredP K (b) at small impact parameters.