Isotope Exchange in Ionised CO2/CO Mixtures: The Role of Asymmetrical C2O3+ Ions

A hitherto unknown, atmospherically relevant, isotope‐exchange reaction was studied in ionised gaseous mixtures containing carbon dioxide and monoxide. The mechanism of the O exchange, proceeding over a double‐minimum potential‐energy surface, was positively established by mass spectrometric and theoretical methods that also allowed the identification and characterisation of the C2O3+ intermediate. The increase of internal energy displaces the observed reactivity towards an endothermic reaction path that involves only CO2 and represents an indirect route to the dissociation of carbon dioxide. CO2+ ions undergo isotope exchange with CO, through a C2O3+ ion of OCOCO connectivity. The reaction efficiency is critically affected by the internal energy deposited into the initially formed C2O3+ adduct, whose decomposition is favoured at higher internal energies with respect to the O exchange occurring through a double‐minimum potential‐energy surface. Under highly energetic conditions, an indirect ulterior route (dashed lines in figure) to dissociation of carbon dioxide into CO and oxygen atoms is provided by the reaction of excited CO2+ ions with CO2.