Using doubly ionized acetylene as a superelectrophilic reagent, the new rare-gas compounds HCCAr2+ and HCCKr2+ have been prepared for the first time in hyperthermal collisions of mass-selected C2H2(2+) with neutral rare gases (Rg). However, electron transfer from the rare gas to the acetylene dication as well as proton transfer from C2H2(2+) to the rare gas efficiently compete with formation of HCCRg2+. The computational investigations show that the formation of HCCRg2+ from acetylene dication is endothermic with Rg = He, Ne, Ar and Kr and only weakly exothermic with Xe. These energetic factors, as well as the pronounced competition with the other reactive channels help to explain why HCCRg2+ is only observed with Rg = Ar and Kr.

The bimolecular reactivity of the CO(2)(2+) dication with neutral CO(2) is investigated using triple quadrupole and ion-ion coincidence mass spectrometry. Crucial for product analysis is the use of appropriate isotope labelling in the quadrupole experiments in order to distinguish the different reactive pathways. The main reaction corresponds to single-electron transfer from the neutral reagent to the dication, i.e. CO(2)(2+) + CO(2) --> 2CO(2)(+); this process is exothermic by almost 10 eV, if ground state monocations are formed. Interestingly, the results indicate that the CO(2)(+) ion formed when the dication accepts an electron dissociates far more readily than the CO(2)(+) ion formed from the neutral CO(2) molecule. This differentiation of the two CO(2)(+) products is rationalized by showing that the population of the key dissociative states of the CO(2)(+) monocation will be favoured from the CO(2)(2+) dication rather than from neutral CO(2). In addition, two bond-forming reactions are observed as minor channels, one of which leads to CO(+) and O(2)(+) as ionic products and the other affords a long-lived C(2)O(3)(2+) dication.

Among the many fascinating results of the Cassini-Huygens mission, the mass spectrum of the ionosphere of Titan has attracted considerable attention. [1] In brief, the ionosphere was found to be surprisingly complex, consisting of hydrocarbon ions C m H n + as well as nitrogen-containing ions C n H n N o + with mass-to-charge ratios up to the probes limit of m/z 100; [2] even much heavier components have been proposed. [1b, 3] While the formation of C m H n compounds with m 7 is reasonably well understood, [3][4][5] routes to larger hydrocarbons are less obvious. Moreover, most of the present models rely on condensation reactions of C m H n + ions with unsaturated precursors such as acetylene, [6] whereas methane, as the major hydrocarbon in the atmosphere of Titan, only plays a minor role in the subsequent growth processes. Here, we report carbon À carbon (C À C) coupling reactions of methane with medium-sized C m H n 2 + dications leading to larger hydrocarbon molecules. Despite low steady-state concentrations of the dicationic intermediates, kinetic modeling allows predictions about the larger hydrocarbon species present in the ionosphere of Titan, thereby rationalizing the results from the Cassini-Huygens mission which consideration of monocations only cannot explain.The activation of methane poses a particular challenge and usually involves energetic conditions or metal catalysis. [7] Under the conditions of the Titan atmosphere (low temperatures and pressures), small hydrocarbon ions can indeed react with methane, but the rate constants decrease with size, and so far reaction 1 involves the largest C m H n + ion reacting with methane under thermal conditions. [8, 9] C 6 H 5Recently, we proposed double ionization as a feasible route for C À C bond formation under extreme conditions. [10] In our laboratory experiments (see Supporting Information), C m H n + mono-and C m H n 2 + dications (m = 7-11, n = 6-12) were generated by electron ionization (EI) of aromatic precursors, mass-selected, and allowed to interact with methane.[11] Whereas most C m H n + monocations studied do not show a significant reactivity with methane under these conditions, many C m H n 2 + dications undergo dehydrogenative C À C coupling according to reaction (2); we note in passing that none of these C m H n 2 + dications reacts with nitrogen as the major component in the atmosphere of Titan.

The destruction of CFC-12 (CF2Cl2) has been studied in an AC, nonthermal, atmospheric pressure plasma reactor packed with barium titanate beads. The extent of the destruction in air ranges between 8% and 40% depending on the conditions. The decomposition products in air as determined by infrared spectroscopy are CO, CO2, and COF2. It is deduced that the undetected chlorine and fluorine is present as F2 and Cl2. A chemical mechanism for the decomposition is proposed. Large concentrations of NO, NO2, and N2O are also formed. Destruction in a stream of pure N2 is about twice as effective as in air under corresponding conditions. The addition of a small amount of water (∼0.03%) or oxygen (∼0.02%) to the nitrogen carrier gas increases the destruction efficiency but the presence of molecular hydrogen (≤2%) brings about no enhancement. It is suggested that in all cases, the primary decomposition step involves dissociative electron attachment to the CF2Cl2. This is confirmed by the observed differences in the destruction in pure nitrogen and in air.

100 years after the prediction of the existence of C2O3 by Berthelot, doubly charged C2O32+ has been identified as a product in the reaction of CO22+ with CO2 (see scheme). The occurrence of this reaction for such a small dication indicates that bond‐forming processes might play a much larger role in reactions of dications than has been anticipated to date.