Hydrogen atom transfer reactions of He+ and Ne+ with H2, D2, and HD

The hydrogen atom transfer reactions of helium(1+) and neon(1+) ions with isotopic molecular hydrogen (H2, D2, and HD) are investigated using guided ion beam techniques. These reactions are exothermic, but are known to be extremely slow at thermal energies. The cross sections for formation of HeH+ (HeD+) and NeH+ (NeD+) exhibit thresholds at high relative translational energies, 8 to 12 eV c.m. Unusual isotope effects are observed in the reaction with HD. The deuteride product is formed exclusively near threshold, while the hydride product predominates at higher energies. Reaction mechanisms involving Rydberg excited states of HeH+2 and NeH+2 are discussed.