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Structure of the integral cross sections for excitation in ion-atom collisions calculated in the plane-wave Born approximation.

We point out that the plane-wave Born approximation sometimes gives rise to a conspicuous minimum of the integral cross section for excitation in ion-atom collisions; for illustration we present results for a transition 1s/sup 2/2s/sup 2/ /sup 1/S..-->..1s/sup 2/2s3p /sup 1/P of berylliumlike ions calculated by using configuration-mixing wave functions. The minimum of the integral cross section arises from a zero of the generalized oscillator strength.