Interference Effects in K Vacancy Transfer of Hydrogenlike S Ions Colliding with Ar

The impact-parameter-dependent K-shell to K-shell vacancy transfer probability has been investigated for 4.7, 7.9, 16, 32 and 90 MeV S 15+-Ar collisions by measuring S and Ar K X-ray particle coincidences. With low-energy H-like S beams (obtained by poststripping S at 108 MeV and decelerating with the Heidelberg RF linac), oscillating Ar K vacancy probabilities as a function of impact parameter were measured. This structure can be interpreted as constructive and destructive interference of the transfer amplitudes on incoming and outgoing parts of the trajectory. Thus measurement of the height as well as the phase of the coupling amplitude allows for a very sensitive test of different coupling models. The interference maxima and minima could be related to values of the phase integral over the 2 p sigma -1 s sigma energy difference from which information about this energy difference could be obtained