Cross sections for the production of excited He⁺ (np) ²P^o states by 50–150-keV proton impact on helium

Cross sections have been measured for the production of He⁺ (np) ²P^o states, n=2,3,4, by proton impact on helium over a projectile velocity range of 1.42–2.45 a.u. (50 ⩽E⩽150 keV). Cross sections were determined by measuring the extreme ultraviolet photons emitted from excited He⁺ ions. The data indicate a lower energy than expected for the maximum cross section. A comparison of the present results in terms of projectile energy dependance with the cross sections for excitation to He (1snp) ¹P^o, ionization, and total electron capture suggests the primary mechanism for the production of excited He⁺ at low energies is transfer excitation, with ionization excitation being the dominant mechanism at higher energies. © 1996 The American Physical Society.