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Summary: Vibrational Mode Effects as a Probe of Inter-channel Coupling in the Reactions of
Formaldehyde Cation with Ammonia and Water
Jianbo Liu, Brady Uselman, Brian Van Devener, and Scott L. Anderson*
Department of Chemistry, 315 S 1400 E, Room 2020, UniVersity of Utah, Salt Lake City, Utah 84112
ReceiVed: May 12, 2004; In Final Form: July 9, 2004
We report the effects of collision energy (Ecol) and five different H2CO+ vibrational modes on reaction of
H2CO+ with ND3 and D2O over the center-of-mass Ecol range from 0.1 to 2.1 eV. Properties of various
complexes and transition states were also examined computationally. For water, the only reaction is proton
transfer (PT), going by a direct mechanism over the entire Ecol range, with a cross section near the collision
limit. H2CO+
vibrational excitation has no effect on reaction with water. Three product channels are observed
in reaction with ammonia. Both proton transfer (PT) and charge transfer (CT) have large cross sections over
the entire energy range. Hydrogen abstraction by H2CO+ from ammonia (HA) accounts for <2% of the total
product signal but is a mechanistically interesting channel. Both PT and HA go by direct mechanisms over
most of the Ecol range, but complex mediation may be important at the lowest energies. All three channels are
mode-specifically affected by H2CO+ vibrational excitation. Vibration controls total reactivity but has essentially
no effect on product branching. Charge transfer during reactant approach appears to have a large effect on
subsequent PT and HA reactions.
I. Introduction
Reactions of H2CO+ with ammonia and water are important
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