Generation of the organo-rare gas dications HCCRg²⁺ (Rg = Ar and Kr) in the reaction of acetylene dications with rare gases

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 C₂H₂²⁺ with neutral rare gases (Rg). However, electron transfer from the rare gas to the acetylene dication as well as proton transfer from C₂H₂²⁺ 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.