Ionization of hydrogen atoms by fast electrons - art. no. 042701

We study ionization of atomic hydrogen by fast electrons using asymptotical ly correct two-center wave functions to describe the scattering system both initially and finally. For the final state, we employ the well-known produ ct wave function of Redmond, which treats all three two-body Coulomb intera ctions exactly, albeit independently. This "3C" wave function is the leadin g term of the exact scattering wave function, regardless of how slow the th ree particles are, if any two particles have large relative separation [Y.E . Kim and A.L. Zubarev, Phys. Rev. A 56, 521 (1997)]. Here we extend the an alysis of Qiu et al. [Phys. Rev. A 57, R1489 (1998)] to show that the 3C wa ve function is the leading term of the exact scattering wave function, rega rdless of how close the three particles are, if any two particles have larg e relative speed. Whereas Brauner, Briggs, and Klar [J. Phys. B 22, 2265 (1 989)], using the above;wave function, demonstrated the importance of final- state two-center effects, we have shown that initial-state two-center effec ts must also be included to obtain accurate results at lower energies [S. J ones and D.H. Madison, Phys. Rev. Lett. 81, 2886,(1998)]. Here we consider three different two-center approximations for the initial state, which yiel d nearly identical results for impact energies above 250 eV. For lower ener gies, the model that uses the eikonal approximation for the initial state e merges as the most accurate one, just as is observed in the, case of ion im pact.