Redetermination of cross sections for formation of metastable He+(2s) ions in fast collisions using an improved calibration procedure

A photoionization chamber has been used to determine the absolute intensity of 304 AA radiation emitted during electric-field quenching of fast He + (2s) metastable ions. The measurements have been used to redetermine with greatly improved accuracy cross sections previously measured in this laboratory for formation of He + (2s) metastable ions by (a) one-electron capture in the passage of 10-60 keV 3 He 2+ ions through H, H 2 , He, Ar, Kr, K, N 2 and O 2 and (b) direct excitation of 6-30 keV 3 He + ions in passage through He, Ar, Kr, H 2 , N 2 and O 2 . The measurements show that, while relative cross sections for the different target gases remain unchanged, previously estimated absolute values should be increased by a factor of 2.2. Cross sections revised in this way are believed to be accurate to within 15% for H 2 and 20% for the other target gases.