Mobilities of O+, O+* and O22+in He and Ar from ion energy distribution measurements in an injected-ion drift tube

An injected-ion drift tube with axial exit orifice feeding a cylindrical electrostatic momentum analyser has enabled ion energy distributions in helium and argon buffer gases to be measured directly. The most probable energies have been used in conjunction with the Wannier relationship to yield mobilities of O + ( 4 S), O + ( 2 D) and O 2 2+ in He over the range 20 to 150 Td and in Ar over the range 70 to 300 Td. Where comparison is possible, good agreement is obtained with recent flow-drift data and Monte Carlo calculations.