Proton scattering from excited states of atomic hydrogen

Abstract

Wavepacket continuum-discretisation approach is used to calculate excitation, ionization and electron-capture (ec) cross sections for proton collisions with n = 2 states of atomic hydrogen, where n is the principal quantum number. The approach assumes a classical motion for the projectile and is based on the solution of the three-body Schrödinger equation using the two-center expansion of the total scattering wave function. The scattering wave function is expanded in an orthonormal basis set built from negative-energy eigenstates and wavepacket pseudostates representing the continuum of both the target atom and the atom formed by the projectile after capturing the electron. With a sufficiently large basis, due to the strong coupling between channels, the method produces converged cross sections for direct-scattering, ionization and ec processes simultaneously. For the quasi-elastic transitions, where both orbital and magnetic quantum numbers change, the integrated cross section is infinite. Nevertheless, the corresponding transitions probabilities are finite at any given impact parameter, indicating that the angular differential cross sections can be measured. Calculated cross sections for scattering on the metastable 2s state are compared with other theoretical results obtained using atomic-orbital close-coupling and classical-trajectory Monte Carlo approaches. Considerable disagreement with previous calculations has been found for some transitions at various incident energies.