Low energy collisions between hydrogen atoms and protons

Slow encounters between H(1s) atoms and H + ions are investigated theoretically, taking into account the coupling between the 2pσ and 2pπ states of the quasi H 2 + molecule. It is found that this coupling makes the cross section for excitation of the second quantum level remarkably large. Calculations are also carried out on the probability P c of electron capture at a fixed (3°) scattering angle and at impact energies E between about 0.25 and 4 keV. The turning points E T on the computed ( P c , E ) curve lie close to those on the corresponding measured curve of Lockwood and Everhart; and P c ( E T ) is not exactly unity or exactly zero as in earlier theoretical work but is instead less than unity or greater than zero in qualitative accord with experiment - quantitative accord would seemingly require allowance for 2pσ-3pσ and perhaps other couplings.