Electronic configuration of O₂

$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\sigma 2p_z^2\pi 2p_y^2{\pi ^*}2p_x^1{\pi ^*}2p_y^1$

Thus the incoming electron will enter in $\pi ^*2p_x$ to form $O_2^+$