Coherent electron impact excitation of the n = 2 states of atomic hydrogen at intermediate energies

A theoretical analysis is given of the parameters M1 + M3, M2 and cos delta which describe the coherent excitation of the n=2 states of atomic hydrogen by intermediate-energy electrons. At small momentum transfers, the parameters M1 + M3 and M2 are dominated by first Born s-p amplitudes, but outside the small-angle region higher-order effects are shown to be very important. The parameter cos delta is also very sensitive to higher-order effects. Unitarised eikonal-Born series results are presented for M1 + M3, M2 and cos delta at incident electron energies of 100, 300 and 350 eV. (author)