Excitation of the helium S levels by hydrogen impact

The cross sections for H(1s)+He(1s 2 1 S) to H( Sigma )+He(1sns 1,3 S), where n=2, 3, 4, 5, or 6, are calculated to first order, with allowance for projectile ionization and projectile-target-electron exchange within the Ochkur-Rudge approximation, as previously described by Bates and Crothers (1967). Accurate helium transition integrals are obtained analytically using Hartree-Fock frozen-core wave functions. There is quite good accord between the calculated 3 3 S and 4 3 S cross sections and the measured values of Van Eck, de Heer and Kistemaker (1964). A discrepancy is noted between the fall-off with respect to energy of the calculated 4 1 S cross section and that of the cross section measured by Robinson and Gilbody (1967). It is suggested that this may be due to neglect of coupling effects. Where appropriate, comparison is made with both proton and electron impact.