Formation of H(2s) and H(2p) in collisions of atomic hydrogen with atomic helium

Abstract
The first Born approximation is used to calculate total cross sections for excitation of the 2s and 2p states of hydrogen by collision with helium. Full account is taken of double excitation processes and the calculations are performed using both length and velocity formulation values of the helium matrix elements. An impact parameter close coupling treatment of the particular process in which the helium atom remains unexcited is carried out with the inclusion of pseudo excited hydrogenic states. The first Born approximation values are in good accord with experiment for energies greater than 10 keV and 30 keV for 2s and 2p excitation, respectively, and, for the lattice case, are in excellent agreement with experiment in the region 40-120 keV where the cross section is almost constant due to the interplay of non-excitation and excitation of the target. At low impact energies, the pseudo-state calculation is an improvement upon previous 4-state calculations but still fails to agree both in shape and in magnitude with experimental data.

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