Ionization of hydrogen atoms by fast electrons

Abstract

We study ionization of atomic hydrogen by fast electrons using asymptotically correct two-center wave functions to describe the scattering system both initially and finally. For the final state, we employ the well-known product wave function of Redmond, which treats all three two-body Coulomb interactions exactly, albeit independently. This “3C” wave function is the leading term of the exact scattering wave function, regardless of how slow the three 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 analysis of Qiu et al. [Phys. Rev. A 57, R1489 (1998)] to show that the 3C wave function is the leading term of the exact scattering wave function, regardless of how close the three particles are, if any two particles have large relative speed. Whereas Brauner, Briggs, and Klar [J. Phys. B 22, 2265 (1989)], using the above wave function, demonstrated the importance of final-state two-center effects, we have shown that initial-state two-center effects must also be included to obtain accurate results at lower energies [S. Jones and D.H. Madison, Phys. Rev. Lett. 81, 2886, (1998)]. Here we consider three different two-center approximations for the initial state, which yield nearly identical results for impact energies above 250 eV. For lower energies, the model that uses the eikonal approximation for the initial state emerges as the most accurate one, just as is observed in the case of ion impact.