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Issue 23, 2010
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Selective dissociation in dication–molecule reactions

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The single electron transfer reactions between 13CO22+ and 12CO2 and between 18O22+ and 16O2 have been studied, using a position-sensitive coincidence technique, to test recently proposed explanations for the preferential dissociation of the 13CO2+ ion (the capture monocation) formed following electron transfer to 13CO22+. In our studies of the carbon dioxide collision system, in agreement with previous work, the capture monocation shows a greater propensity to dissociate than the monocation formed from the neutral, 12CO2+ (the ejection monocation). The coincidence data clearly show that the dissociation pathways of the 13CO2+ and 12CO2+ ions are different and are consistent with the ejection monocation dissociating via population of the C2Σ+g state, whilst the capture ion is predominantly directly formed in dissociative quartet states. This state assignment is in accord with an expected preference for one-electron transitions in the electron transfer process. A propensity for one-electron transitions also rationalizes our observation that following dissociative single electron transfer between 18O22+ and 16O2 the ejection monocation (16O2+) preferentially dissociates; the opposite situation to that observed for carbon dioxide. The coincidence results for this reaction indicate the 16O2+ dissociation results from population of the B(2Σg) state. The less favoured dissociation of the capture monocation clearly involves population of a different electronic state(s) to those populated in the ejection ion. Indeed, the experimental data are consistent with the dissociation of the capture monocation via predissociated levels of the b(4Σg) state. Since the population of the B(2Σg) state from the neutral O2 molecule involves a one-electron transition, and the population of the valence dissociative states of O2+ from the dication are multi-electron processes, the preferential dissociation of the ejection monocation in this collision system can be rationalized by the same principles used to explain the electron transfer reactivity of CO22+ with CO2.

Graphical abstract: Selective dissociation in dication–molecule reactions

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Publication details

The article was received on 10 Dec 2009, accepted on 17 Mar 2010 and first published on 15 Apr 2010

Article type: Paper
DOI: 10.1039/B926049H
Citation: Phys. Chem. Chem. Phys., 2010,12, 6233-6243
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    Selective dissociation in dication–molecule reactions

    M. A. Parkes, J. F. Lockyear, S. D. Price, D. Schröder, J. Roithová and Z. Herman, Phys. Chem. Chem. Phys., 2010, 12, 6233
    DOI: 10.1039/B926049H

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