Dynamics of the ion–molecule reaction Kr+(H2,H)KrH+

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/65/4/10.1063/1.433219

Role of impact parameter in branching reactions

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/63/11/10.1063/1.431205

Observation of a translational energy threshold for a highly exoergic ion‐molecule reaction

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/60/9/10.1063/1.1681592

Role of impact parameter in branching reactions: Chemical accelerator studies of the reaction Xe++CH4→XeCH3 ++H

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/74/9/10.1063/1.441716.Integral reaction cross sections and product velocity distributions have been measured for the ion–molecule reaction Xe+(CH4,H)XeCH3 + over the relative reactant translational energy range of 0.7–5.5 eV by chemical accelerator techniques. The kinematic results indicate that reaction proceeds in a direct manner by a rebound mechanism over the energy range studied, suggesting that this substitution reaction occurs predominantly in small impact parameter collisions. This finding contrasts with the results obtained for the competing reaction, Xe+(CH4,CH3)XeH+, where the strong forward scattering of the XeH+ product indicates that H‐atom abstraction occurs primarily in large impact parameter collisions

Translational energy dependence of reaction mechanism: Xe++CH4→XeH++CH3

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/74/9/10.1063/1.441715.The dynamics of the exoergic ion–molecule reaction Xe+(CH4,CH3)XeH+ were studied by chemical accelerator techniques over the relative translational energy range 0.2 to 8 eV. Results of the kinematicmeasurements are reported as scattering intensity contour maps in Cartesian velocity space. Center‐of‐mass angular and energy distributions, derived from these maps, provide information on the reaction mechanism and on the partitioning of available energy between internal and translational modes in the products. The results suggest that reaction proceeds via the formation of a long‐lived complex at low collision energies (below 0.5 eV) and by a direct mechanism approaching spectator stripping at higher energies

Observation of a stripping threshold for the reaction N2 ^++CH4→N2H^++CH3

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/64/9/10.1063/1.432690Chemical accelerator studies on isotopic variants of the reaction N2 ++CH4→N2H++CH3 are reported. Reaction cross sections, as well as velocity and angular distributions of the ionic products have been measured as a function of initial translational energy over the energy range 0.65–35 eV (center of mass). The results are similar to those recently reported for the reaction of Ar+ with CH4. The excitation function maximizes at about 5 eV (c.m.) and decreases at lower collision energies, appearing to possess a threshold at 0.1 eV. At the higher energies there is a large isotope effect favoring abstraction of H over D. The product velocity vector distribution is strongly peaked forward of the center of mass, indicating that the reaction is predominantly direct over the energy range studied. The spectator stripping model, although providing a reasonable first approximation to the reaction dynamics, overestimates the product translational energy by approximately 0.1 eV. This behavior is presumed to be caused by a basin in the potential energy hypersurface for this reaction. If, however, an N2CH4 + complex is formed at low collision energies, it appears to decompose via reaction channels other than that resulting in N2H+ formation

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

Chemical accelerator studies of reaction dynamics: Ar^+ + CH4 → ArH^+ + CH3

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/62/7/10.1063/1.430836.Chemical accelerator studies on isotopic variants of the reaction Ar+ + CH4 → ArH+ + CH3 are reported. Velocity and angular distributions of the ionic product as a function of initial translational energy have been measured over the energy range 0.39–25 eV center-of-mass (c.m.). The asymmetry of the product distribution with respect to the center of mass indicates that the reaction is predominantly direct over the energy range studied. The dynamics of the reaction are approximated by the spectator stripping model: The reaction exothermicity appears as product internal energy and product excitation increases with collision energy at the rate predicted by this model. The internal degrees of freedom of the neutral product have little effect on reactiondynamics, and product excitation appears to reside principally in the ionic product. Deviations from the spectator stripping model suggest the existence of a basin in the potential energy hypersurface for this reaction; the ArCH4 + complex which may be formed at low collision energies, however, preferentially decomposes via reaction channels other than that resulting in ArH+ formation