Selective dissociation in dication–molecule reactions

Abstract

The single electron transfer reactions between (13)CO(2)(2+) and (12)CO(2) and between (18)O(2)(2+) and (16)O(2) have been studied, using a position-sensitive coincidence technique, to test recently proposed explanations for the preferential dissociation of the (13)CO(2)(+) ion (the capture monocation) formed following electron transfer to (13)CO(2)(2+). 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, (12)CO(2)(+) (the ejection monocation). The coincidence data clearly show that the dissociation pathways of the (13)CO(2)(+) and (12)CO(2)(+) ions are different and are consistent with the ejection monocation dissociating via population of the C(2)Sigma 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 (18)O(2)(2+) and (16)O(2) the ejection monocation ((16)O(2)(+)) preferentially dissociates; the opposite situation to that observed for carbon dioxide. The coincidence results for this reaction indicate the (16)O(2)(+) dissociation results from population of the B((2)Sigma) 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((4)Sigma) state. Since the population of the B((2)Sigma) state from the neutral O(2) molecule involves a one-electron transition, and the population of the valence dissociative states of O(2)(+) 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 CO(2)(2+) with CO(2).

Energy Partitioning in Single-Electron Transfer Events between Gaseous Dications and Their Neutral Counterparts

“…In addition, already in these initial experiments much more DET was observed for the dication {Reaction [3(a)]} than for the neutral compound {Reaction [3(b)]}, which was further backed up by an earlier study. 58 These observations indeed support the simple explanation put forward in Scheme 1 but, in order to not just support, but really cross-check this scheme, this particular reaction was studied in great detail, including extensive isotopic labeling, 57,59 various advanced experimental techniques, such as angle-resolved scattering experiments 60 and coincidence studies 59,61 and even more complete theoretical investigations of the already extensively investigated potential-energy surfaces of CO 2 n+ (n = 0-2). 62 It is, in fact, the combination of the various experimental and theoretical techniques which provides not only a very deep insight into the collision process but, in its synthesis, an almost complete understanding of the reactions observed as a synergistically added value.…”

Bond-forming and electron-transfer reactivity between Ar2+ and O2

“…precursor velocity, the KER for the dissociation of O into O + + O can also be extracted from our data 69. This exoergicity for the O 2 + dissociation, from the high source field experiment, is shown in Fig.…”

“…Using , in a similar experiment, revealed a dominant peak in the exoergicity spectrum at 1.5-3.0 eV, this overlaps with the lower end of the maximum exoergicity observed in this study. 69 (c 4 S À u ) to the lowest energy dissociation limit of O + + O. 52,53,66,70 In order to explain the higher energy exoergicities, higher lying states of O 2 + must be involved.…”

Structural Properties of Gas-Phase Molybdenum Oxide Clusters [Mo4O13]2−, [HMo4O13]−, and [CH3Mo4O13]− Studied by Collision-Induced Dissociation

“…Therefore, the energies represent also a lower limit of the energy barrier to overcome during fragmentation. For singly charged fragments, however, the reverse Coulomb barrier must be added, since Coulomb explosion is associated with significant kinetic energy release [41, 42, 50–52]. We estimated the barrier based on a point-charge separation of 4.1 Å at the transition state of Coulomb explosion, which corresponds to the molecule diameter.…”