The dissociative electroionization of carbon dioxide by low-energy electron impact. The C+, O+ and CO+ dissociation channels

Abstract

This work reports the dissociative ionization of CO 2 between 19 and 40 eV. The three dissociation channels producing C + , O + and CO + are examined in detail. Translational energy distributions as a function of the impinging electron energy and the ionization efficiency for fixed minimum kinetic energy carried by the fragments are measured. The kinetic energy versus appearance energy diagram is obtained for the three fragment ions. When available, the present results are compared with previous measurements. The lowest appearance energy of O + and CO + corresponds to the predissocia-tion of the CO 2 + (C 2 Σ g + ) state. At higher energies, all the fragment ions are exclusively produced by the dissociative ionization of CO 2 in the multiple electron transition (MET) states. Predissociation is most probably the dominant mechanism. Each MET state branches off to produce not only the three fragments, but also the same fragment in two different states. This is observed for each dissociation channel, i.e. O + , CO + and/or C + . In the latter channel no evidence is found for the dissociative ionization reaction CO 2 + → C + + 2O.

The dissociative ionization of carbon dioxide below 21.22eV. A high resolution PIPECO spectroscopic investigation

“…A weak He + ion signal is observed at m/z 4. These translational energy distribution results could only be compared with our previous electron impact data [1]. The kinetic energy versus appearance energy diagrams of O + and CO + show 400 meV ions for both species at 21.2 eV electron energy.…”

“…The literature on this subject has been reviewed recently [1]. By high resolution photoionization mass spectrometry and threshold photoelectron spectroscopy the major importance of autoionization in the appearance of O + and CO + has been demonstrated [2][3][4][5].…”

“…Previously, we reported a detailed study of the dissociative electroionization of CO 2 in its three dissociation channels, covering the electron energy range from 19 to 40eV [1]. This investigation included the experimental determination of the translational energy of the fragment ions at threshold.…”

“…In the latter case, the investigation was limited to the production of O + and CO 2 + only. The experiments covering the three dissociative ionization channels of CO 2 into CO + , O + and C + mainly used the electroionization mass spectrometric technique [1]. The energies range from the onset up to l00eV impinging electron energy.…”

“…Using synchrotron radiation, these three fragmentation channels were investigated by mass spectrometric photoionization between 35 and 60eV photon energy [8]. There are very few studies which include the translational energy measurements of the fragment ions [1].…”