Electron Capture in Collisions between Protons and Hydrogen Atoms

Cross sections have been determined for electron transfer as well as direct excitation and ionization in $p$-H collisions using the symmetric double-center Sturmian bases $\leq 16 (s,p,d)$ on each center (176 states in all) and $\leq 13(s,p,d,f)$ on each center (220 states in all) for proton energies $1-100$ keV, substantially expanding pioneering Sturmian calculations carried out thirty years ago.\footnote{R.Shakeshaft, J. Phys. B {\bf 8}, 1114 (1975); Phys. Rev. A {\bf 18}, 1930 (1978).} At energies $100-1000$ keV, Sturmian calculations have been carried out with the asymmetric basis $\leq 30(s,p,d,f)$ centered on the target nucleus and only $1s$ centered on the projectile. The computer code for arbitrary nuclear charges, recently applied to $\alpha$-H collisions,\footnote{T.G. Winter, Phys. Rev. A {\bf 76}, 062702 (2007).} has been specialized to the homonuclear case, halving the computing time. The results may be compared with large basis, double-center Gaussian results\footnote{N. Toshima, Phys. Rev. A {\bf59}, 1981 (1999).}; triple-center results\footnote{T. G. Winter and C.D. Lin, Phys. Rev. A {\bf29}, 567 (1984).}; double-center, even-tempered basis results\footnote{J. Kuang and C. D. Lin, J. Phys. B {\bf29}, 1207 (1996).}; other theoretical results; and numerous experimental results.