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Vibrational and collision energy effects on the reaction with methanol

Summary: Vibrational and collision energy effects on the reaction
of CH3CHOż
with methanol
Ho-Tae Kim, Jianbo Liu, and Scott L. Anderson
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112
Received 17 May 2001; accepted 11 July 2001
Integral cross sections and product velocity distributions were measured for reaction of
acetaldehyde cation with methanol over a center-of-mass collision energy range from 0.1 to 2.2 eV.
Reactivity is dominated by exoergic proton transfer PT , which is strongly suppressed by collision
energy, and mildly suppressed by CH3CHO vibrational excitation. PT is complex-mediated at low
energies, switching to a direct stripping mechanism at high energies. Of the two possible PT
channels, it appears that transfer of the aldehyde proton dominates. Hydrogen abstraction HA is a
minor channel at low collision energies, also complex-mediated. Abstraction is observed from both
hydroxyl and methyl sites on methanol, and the two channels have different, and counterintuitive
collision energy dependence. Despite being exoergic, with no barriers, the HA channel shows
apparent threshold behavior, attributed to competition with the dominant PT channel. The
competition indicates that different intermediate complexes must interconvert efficiently, at least for
low collision energies. At low energies, HA is strongly enhanced by collision energy, while
vibrational excitation has no effect. Finally, there is a minor product channel corresponding to
methyl elimination ME from a complex. Despite a relatively complicated reaction coordinate, the


Source: Anderson, Scott L. - Department of Chemistry, University of Utah


Collections: Energy Storage, Conversion and Utilization; Materials Science; Chemistry