Reactions of H2 with He, Ne, and Ar

The two reactions of H2 with He and Ne that have been studied in some detail by photoionization mass spectrometry  

They are of special interest since they are both endoergic for ground-state reactants but are observed to occur at thermal energies for vibration-ally excited H2 ions above a critical energy. The vibrational energy 

The reaction of H2 with Ar is exothermic for ground-state reactants, and the cross section shows little if any variation with vibrational energy. In spite of the closeness of the two ionization thresholds, the photoionization data (Fig. 6) show very clearly that ArH is formed by reaction of Ar ions with H2 as well as by H2 with Ar. It is also readily seen from the data that the Pi/2 excited state of the Ar ion reacts with somewhat higher cross section than the ground state. 

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