CROSS-SECTIONS FOR THE PRODUCTION OF EXCITED HE-2(0) STATES BY 50-150-KEV PROTON IMPACT ON HELIUM( (NP) P)

Cross sections have been measured for the production of He+ (np) P-2(o ) states, n = 2,3,4, by proton impact on helium over a projectile velo city range of 1.42-2.45 a.u. (50 less than or equal to E less than or equal to 150 keV). Cross sections were determined by measuring the ext reme ultraviolet photons emitted from excited He+ ions. The data indic ate a lower energy than expected for the maximum cross section. A comp arison of the present results in terms of projectile energy dependance with the cross sections for excitation to He (1snp) P-1(o), ionizatio n, and total electron capture suggests the primary mechanism for the p roduction of excited He+ at low energies is transfer excitation, with ionization excitation being the dominant mechanism at higher energies.