Spin-orbit state-selected reactions of Kr+(2P3/2 and 2P1/2) with H2, D2, and HD from thermal energies to 20 eV c.m.

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Abstract
Spin-orbit state-selected reactions of Kr+(2PJ), J=3/2 and J=1/2, with isotopic molecular hydrogen (H2, D2, and HD) to form KrH+ and KrD+ are investigated using guided ion beam techniques. Reaction cross sections for each spin-orbit state are measured as a function of the relative translational energy of the reactants from near thermal energies up to 20 eV c.m. At low energies, the cross sections for reaction with H2 and D2 are each about 2.6 times larger for the 2P3/2 ground spin-orbit state of krypton ion than for the 2P1/2 excited state. For the HD reaction, the 2P3/2 reactivity is enhanced by a factor of about 4.2. A higher-energy process, which exhibits an apparent activation energy of about 1 eV, is present only for the 2P3/2 spin-orbit state. The Kr+(2P3/2) spin-orbit state exhibits a strong intermolecular isotope effect, showing the unusual dependence σ(HD)>σ(H2)>σ(D2) for the total reaction cross sections at low energies. Cross sections for the Kr+(2P1/2) state show a much smaller dependence on the hydrogen isotope. The intramolecular isotope effect for the individual KrH+ and KrD+ channels in the reaction with HD shows several reversals over the energy range studied. These results are discussed in terms of the potential energy surfaces of the krypton–hydrogen system.