Potential energy surfaces describing ion complexes containing molecular hydrogen

High-level ab initio molecular orbital calculations have been carried out to describe the potential energy surfaces for a series of systems corresponding formally to dimer ions of molecular hydrogen with an inert-gas atom or a first- or second-row hydride [X⋅⋅⋅H2]̇ +, where X=He, Ne, Ar, Kr, HF, HCl, H2O, H2S, NH3, and PH3. Of the [XH2]̇ + ion complexes, [Ne⋅⋅⋅H2]̇ +, [Ar⋅⋅⋅H2]̇ +, [Kr⋅⋅⋅H2]̇ +, and [HFH⋅⋅⋅H]̇ + lie in wells of significant depth and should be experimentally observable. The energetics of ion–molecule reactions associated with the [XH2]̇ + systems have been examined in detail. The reactions include proton- and hydrogen-transfer reactions and hydrogen-exchange reactions. Pathways and transition structures for scrambling of hydrogen atoms within the [XH2]̇ + complexes, some of which are relevant to the exchange reactions, have also been determined.