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Reaction of formaldehyde cation with methane: Effects of collision energy and methane vibrations

Summary: Reaction of formaldehyde cation with methane: Effects of collision energy
and H2COż
and methane vibrations
Jianbo Liu, Brian Van Devener, and Scott L. Andersona)
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112
Received 20 February 2003; accepted 3 April 2003
The effects on the title reaction of collision energy (Ecol), five H2CO vibrational modes, and
deformation vibrations of methane have been studied, including the measurement of product integral
and differential cross sections over a center-of-mass Ecol range from 0.09­3.3 eV. Electronic
structure and RRKM calculations are reported, providing an additional mechanistic insight. The
total reaction efficiency is well below unity, despite there being two exoergic reaction pathways with
no activation barriers. The energetically more favorable channel corresponds to H elimination HE
from an intermediate complex, however, this channel accounts for only 15% of the total reaction
cross section at low Ecol and is negligible at high energies. The dominant channel, hydrogen
abstraction HA by H2CO from methane, is dominated by a complex-mediated mechanism at low
Ecol , switching over to a direct hydrogen-stripping mechanism at high Ecol . Both HA and HE are
inhibited in a strongly mode-specific fashion by H2CO vibrational excitations, and greatly
enhanced by excitation of methane deformation vibrations. The strong mode specificity indicates
that the reaction-limiting step occurs early in the collisions. © 2003 American Institute of Physics.
DOI: 10.1063/1.1577312


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


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