Effect of exchange on the binary-encounter-electron double-differential cross section inCq+-H2collisions at 0.75 MeV/amu

The production of binary-encounter electrons in collisions of ${\mathrm{C}}^{\mathit{q}+}$ ions with molecular hydrogen has been studied at an impact energy of 0.75 MeV/amu. The measured double-differential cross section (DDCS) at a forward angle (${\mathrm{\theta }}_{\mathrm{lab}}$=0), with respect to the beam direction, is in excellent agreement with the theoretical cross sections evaluated in the impulse approximation by using the elastic-electron–ion differential cross section with the Compton profile of the target electrons. The theoretically calculated DDCS is extremely sensitive to the impact energy. Hence a precise measurement of the projectile beam energy is required to compare predicted values with the data. The agreement between theory and experiment demonstrates the importance of exchange in the description of binary-encounter electrons and that the exchange increases with the number of electrons on the projectiles.