Excitation cross sections of atoms and ions by electrons are rapidly decreasing with the increase of &Deltal, where &Deltal is the change of the orbital quantum number. For example, the threshold cross sections for 1s - 4l transitions in He⁺ ion without exchange are equal to 3.1, 9.9, 0.94 and 0.02 (in units of 100 &pi a₀²) for l = 0, 1, 2 and 3, respectively. This decrease is caused by the small value of matrix element of (r_</r_>)^&kappa+1 operator, where &kappa is multipolarity.
The role of exchange is drastically increasing with the increase of &Deltal. This effect results from the fact that the direct part of the transition (&kappa=&Deltal) decreases more rapidly than the exchange part which includes small &kappa&ne&Deltal. For &Deltal = 3, the exchange amplitude becomes much larger than the direct one.
In the present work, this effect is considered in the frame of the first order perturbation theory. The amplitudes and the cross sections are calculated in Coulomb-Born approximation with accounting for exchange (CBE) and without it(CB). For account of exchange the orthogonalized function method [1] is used. To study the influence of the channels interaction on the considered effect the K-matrix method is also used for the calculations.

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