EXCITATION OF AUTOIONIZING STATES OF HELIUM IN COLLISIONS WITH PROTONS - VALIDITY OF THE 1ST BORN APPROXIMATION

We have performed coupled-channel computations of the cross section fo r excitation of the 2s2p 1P resonance in collisions between ground-sta te helium atoms and protons, in the range of impact energies 0.5 less- than-or-equal-to E(p) less-than-or-equal-to 3 MeV. For the first time in such computations, the coupling of the doubly-excited state to the continuum has been taken into account. Comparison with the equivalent first-order calculations confirms that the Born approximation is not v alid for E(p) < 0.5 MeV.