Summary: International Journal of Mass Spectrometry 241 (2005) 173184
Dynamical control of `statistical' ionmolecule reactions
Jianbo Liu, Scott L. Anderson
Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, UT 84112-0850, USA
Received 11 November 2004; accepted 7 December 2004
Experimental and theoretical studies of two ionmolecule reactions are reviewed. The reactions of H2CO+
with methane are
both mediated by long-lived complexes at low collision energies. The complex lifetimes, product recoil energy and angular distributions, and
product branching ratios are all in good agreement with predictions based on statistical decay of the intermediate complexes. Nonetheless, it
is clear that both reactions are, in fact, controlled by dynamical effects. In particular, reactivity is strongly and mode-specifically dependent on
the vibrational state of the reactants, whereas a statistical mechanism would depend only the energy content of the vibrations. The vibrational
effects reflect the dynamics involved in the formation and decay of weakly bound precursor complexes, before the collisional interaction can
scramble the initial state information.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Ionmolecule reaction dynamics; Vibrational effects; Precursor complex
Many ionmolecule reactions are assumed to go via mech-