Controlling bimolecular reactions: Mode and bond selected reaction of water with hydrogen atoms
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706 (US)
Vibrational overtone excitation prepares water molecules in the {vert bar}13{r angle}{sup {minus}}, {vert bar}04{r angle}{sup {minus}}, {vert bar}12{r angle}{sup {minus}}, {vert bar}02{r angle}{sup {minus}}{vert bar}2{r angle}, and {vert bar}03{r angle}{sup {minus}} local mode states for a study of the influence of reagent vibration on the endothermic bimolecular reaction H+H{sub 2}O{r arrow}OH+H{sub 2}. The reaction of water molecules excited to the {vert bar}04{r angle}{sup {minus}} vibrational state predominantly produces OH({ital v}=0) while reaction from the {vert bar}13{r angle}{sup {minus}} state forms mostly OH({ital v}=1). These results support a spectator model for reaction in which the vibrational excitation of the products directly reflects the nodal pattern of the vibrational wave function in the energized molecule. Relative rate measurements for the three vibrational states {vert bar}03{r angle}{sup {minus}}, {vert bar}02{r angle}{sup {minus}}{vert bar}2{r angle}, and {vert bar}12{r angle}{sup {minus}}, which have similar total energies but correspond to very different distributions of vibrational energy, demonstrate the control that initially selected vibrations exert on reaction rates. The local mode stretching state {vert bar}03{r angle}{sup {minus}} promotes the H+H{sub 2}O reaction much more efficiently than either the state having part of its energy in bending excitation ({vert bar}02{r angle}{sup {minus}}{vert bar}2{r angle}) or the stretching state with the excitation shared between the two O--H oscillators ({vert bar}12{r angle}{sup {minus}}). The localized character of the vibrational overtone excitation in water has permitted the first observation of a bond selected bimolecular reaction using this approach.
- OSTI ID:
- 5775111
- Journal Information:
- Journal of Chemical Physics; (USA), Vol. 94:7; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
HYDROGEN
CHEMICAL REACTIONS
WATER
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
EXCITATION
VIBRATIONAL STATES
ELEMENTS
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
HYDROGEN COMPOUNDS
KINETICS
NONMETALS
OXYGEN COMPOUNDS
REACTION KINETICS
400201* - Chemical & Physicochemical Properties