Single-electron capture by slow protons in helium

The perturbed stationary state method is applied to He(1s 2 )+H + -> He + (1s)+H(1s) but with neglect of momentum transfer. The calculations of Green et al. and of Sin Fai Lam show that the approximation is certainly untenable at energies above 16 keV. The experimental results of Hasted and Stedeford and of Stier and Barnett for the sum total of all processes involving charge transfer from helium to protons are exceeded from 3 to 10 keV. The differential cross section at small angles of deflection compares reasonably well with the experiments of Helbig and Everhart for energies below 5 keV.