Chemical accelerator studies of isotope effects on collision dynamics of ion–molecule reactions: Kr++HD

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/67/10/10.1063/1.434631.The reaction of Kr+ with HD has been studied as a function of relative collision energy over the range 0.08–3.1 eV (c.m.) by measuring integral reaction cross sections and the velocity vector distributions of product ions formed when a collimated, energy selected beam of Kr+ impinges on HD under single collision conditions. The ratio σ (KrH+)/σ (KrD+) passes through a sharp maximum (?2.5) at about 0.7 eV relative collision energy and decreases by a factor of 10 at higher energies. The isotopic product velocity vector distributions show a high but not perfect degree of symmetry about the center of mass at low energies but are extremely anisotropic at high energies, with the KrH+ being strongly forward scattered and the KrD+ being back scattered

Excitation functions for the reactions of Ar^+ with CH4, CD4, and CH2D2

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/63/11/10.1063/1.431267.Integral reaction cross sections as a function of initial translational energy (0.4–30 eV c.m.) are reported for isotopic variants of the exoergic ion‐molecule reaction Ar++CH4 → ArH++CH3. The excitation functions, which maximize at about 5 eV and decrease at lower collision energies, appear to possess translational energy thresholds at about 0.1 eV. At the higher energies there is a large isotope effect favoring abstraction of H over D. The observed threshold behavior, unusual for exoergic reactions of positive ions, is discussed in terms of the formation of an ArCH4 + intermediate complex at low collision energies