Chemi-ionization and secondary ion reactions in molecular hydrogen and its isotopes on impact of metastable helium atoms

Relative cross sections for the following reactions are reported: He*(2'S,23S) + X2 → X2+ + He + e → HeX+ + X + e → HeX2+ + e in which X2 is(a) H2, (b) D2, and (c) HD. The isotope effect in the production of HeH+ and HeD+ in Reaction (2c) was determined and relative measurements were made of the kinetic energy of the ion product in Reaction (1). The cross section for the secondary reaction H2+ + H2 → H3+ + H was also determined as a function of the relative kinetic energy of the reactants. This energy-dependent cross section was determined for H2+ formed both by helium metastable atom collisions and by electron impact. The cross section for H+2 formed by metastable helium was found to be greater than for H+2 formed by electron impact. This may be evidence for an additional reaction producing H+3 involving highly excited Rydberg states of H2 as reactants. (auth)