Role of Multistep Processes in Heavy-Ion Inner-Shell Excitations

This Letter discusses inner-shell excitation in collisions of very heavy ions ($Z_1+Z_2\gtrsim 140$) in the framework of the quasimolecular model. The importance of multistep excitations and of coupling between continuum states is demonstrated. The $1s\sigma$ vacancy probabilities resulting from coupled-channels calculations exceed perturbation theory by a factor 3-5, thus giving good agreement with recent experimental results.