ABUNDANCE OF EXCITED IONS IN 0+ AND 02+ ION BEAMS

A method has been developed to determine the fraction of excited ions present in an ion beam formed using various energies Es of the electrons in the ion source. The determination is made ∼20 /μsec after formation of the ions so that only long-lived states remain in the beam, as is usual in beam experiments. The method consists of attenuating the ion beam in a gas-filled reaction chamber, where different states of the ions suffer different attenuations. Results have been obtained for O2+ and O+ ion beams. In each case only one excited state appears to be important: For O2+ the fraction f of this excited state was found to be 0.22, 0.30, and 0.33 for Es values of 25 eV, 50 eV, and 100 eV, respectively. For O+, f is 0.27 for Es = 50 eV and 0.30 for Es= 100 eV. The use of these results is illustrated by combining them with crossed-beam measurements of charge transfer to determine separately the cross sections for the ground state and the excitedstate ions of O+ and O2+.