Yield, u, of the peaks with m/q ratio of 16 (O+ and ) and 32 ( ) for several delay times, normalized to their respective yields, u 0, at a minimum delay time of 600 ns. The lines crossing the experimental data points represent the sum of all the distributions present for each group peak in order to accomplish the best possible fit, using the DETOF technique. The same Maxwell-Boltzmann (MB) distribution used to fit the experimental data for the parent ion is present, properly weighted, in the data for the m/q = 16 peak, corresponding to the . It should be stressed that using only the Exponential (Expo) and Gaussian (G) distributions is not enough to correctly fit the experimental data.
Ratio between the oxygen molecule dication and its parent ion. It can be clearly seen that this ratio does not feature a descent with the increase of the electron impact energy, for the measured energy range, as would be expected for a sequential double ionization. This indicates that the most likely process for the dication formation could be a single ionization followed by an Auger-like process. Error bars indicate calculated uncertainties below 18% for 41 and 45 eV and up to 15% for the remaining measured electron energies.
Double ionization cross sections for the oxygen molecule, given in Mb. The data were corrected by the MCP detector efficiency and the transmission efficiency of the TOF setup. Uncertainties are estimated to be 15% for and 5% for O+ and .
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