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Summary: Vibrational mode and collision energy effects on reaction of H2CO+
with C2H2: Charge state competition and the role of Franck-Condon factors
in endoergic charge transfer
Jianbo Liu, Brian Van Devener, and Scott L. Andersona
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112
Received 28 September 2005; accepted 4 October 2005; published online 28 November 2005
The effects of collision energy Ecol and six different H2CO+
vibrational states on the title reaction
have been studied over the center-of-mass Ecol range from 0.1 to 2.6 eV, including measurements of
product ion recoil velocity distributions. Ab initio and Rice-Ramsperger-Kassel-Marcus calculations
were used to examine the properties of complexes and transition states that might be important in
mediating the reaction. Reaction is largely direct, despite the presence of multiple deep wells on the
potential surface. Five product channels are observed, with a total reaction cross section at the
collision limit. The competition among the major H2
+
transfer, hydrogen transfer, and proton transfer
channels is strongly affected by Ecol and H2CO+
vibrational excitation, providing insight into the
factors that control competition and charge state "unmixing" during product separation. One of the
more interesting results is that endoergic charge transfer appears to be controlled by Franck-Condon
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