Electron capture into excited states of helium by helium-ion impact on helium

Cross sections for electron capture into each excited state of He up to 4 1,3D by He+ impact on He in the energy range 100--10 000 keV have been calculated by means of the first Born approximation (Bates's version). A Gaussian technique previously developed for evaluating two-center integrals occurring in the Born amplitude has been used. One-parameter, variational wave functions are derived for each excited state of helium up to 4 1,3D. Some of the excited 1S cross sections are found to be affected by almost a factor of 2 by the choice of 1 1S helium wave function and orthogonality of the excited state 1S functions to this function. The observed departure of the ratio of triplet to singlet cross sections from the statistical weight of three is related partly to the interference between a one-electron process of capture into an excited state of helium and a two-electron process of capture into the ground state with the original He+ electron excited, and is related partly to the difference between the variational singlet and triplet excited one-electron wave functions. At energies of about 100 keV, agreement with available experimental results is generally good; however, for the 3 1P, 4 1P, and 4 1D states, the disagreement exceeds the estimated experimental uncertainty