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Absolute cross sections for O2 dication production by electron impact
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Image of FIG. 1.
FIG. 1.

Yield, , of the peaks with m/q ratio of 16 (O and ) and 32 ( ) for several delay times, normalized to their respective yields, , 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.

Image of FIG. 2.
FIG. 2.

Absolute cross sections for the production of (a) and (b) the group O + , for different electron impact energies: present data, black filled squares; Straub , blue lozenges; Tian and Vidal, red circles; Krishnakumar and Srivastava, pink triangles; and Märk, green stars.

Image of FIG. 3.
FIG. 3.

Double ionization cross sections for the oxygen molecule: open symbols, Märk's data for OO ; closed symbols, present work, for . The error bars displayed for the present work correspond to the combined estimated errors of the experimental setup and the DETOF technique.

Image of FIG. 4.
FIG. 4.

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.


Generic image for table
Table I.

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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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Absolute cross sections for O2 dication production by electron impact