Critical Review of Rate Constants for Reactions of Hydrated Electrons,
Hydrogen Atoms and Hydroxyl Radicals
(.OH/.O–) in Aqueous Solution
George V. Buxton
University of Leeds,
Cookridge Radiation Research Centre,
Leeds, LS16 6QB, England
and
Clive L. Greenstock
Medical Biophysics Branch,
Whiteshell Nuclear Research Establishment,
Atomic Energy of Canada Limited Research Company,
Pinawa, Manitoba, Canada, ROE 1LO
and
W. Phillip Helman and Alberta B. Ross
Radiation Chemistry Data Center,
Radiation Laboratory,
University of Notre Dame,
Notre Dame, IN 46556
J. Phys. Chem. Ref. Data 17: 513-886 (1988)
Kinetic data for the radicals H. and .OH in aqueous solution,
and the corresponding radical anions, .O– and eaq–, have
been critically reviewed. Reactions of the radicals in aqueous solution have
been studied by pulse radiolysis, flash photolysis and other methods. Rate
constants for over 4400 reactions, more than 6100 measured values are tabulated,
including reactions with molecules, ions and
other radicals derived from inorganic and organic solutes.
The accompanying data is based on the collection reported in the above publication
and additional data collected through 1995.
Separate lists are provided for reactions of the
hydrated electron,
hydrogen atom,
hydroxyl radical and
oxide radical ion.
Only rate data at ambient temperature in aqueous homogeneous solution, for
which normal diffusion theory applies have been included.
Data involving deuterated
species have been included but rate constants in D2O solution have been omitted
(that is, reactions of ed–, D., .OD are omitted). Unpublished or
unrefereed data have been omitted unless
sufficient details were available so that the data could be evaluated.
Estimated or single values, upper and lower limits have only been included
in the absence of more definitive data. Ambiguous data reported for mixtures of
different solutes or different forms of one solute were not knowingly included.
In certain cases, pKa values or other pertinent information have been included under
`comments' when available.
Arrangement of Reactants:
Lists are arranged similarly with the inorganic reactants listed
first, grouped alphabetically by main element. Within the groupings by element the
arrangement is in order of increasing oxidation state. Within a particular
oxidation state for a metal, aquated ions are listed first followed by
complexes with neutral ligands (amines). Complexes with anionic inorganic
ligands are listed next, followed by complexes with anionic organic ligands,
such as carboxylic acids, amino acids and peptides; polynuclear metal
species are listed last. The metal ions are generally shown without ligated
water (see below). The inorganic reactants are followed by the organic
reactants, arranged alphabetically by name.
Each entry in the lists is the name of the reactant and a link to its data page.
Systematic names are used in the lists for the substrates unless the reactant
has a complex structure or is better known by a common name (e.g. Camphor
rather than 1,7,7-Trimethylbicyclo[2.2.1]heptan-2-one).
Reactions:
The reactions use
line formulae whenever they are available in the
registry file and when space allows; otherwise, abbreviations or symbols,
or in some cases the molecular formula, have
been used. Reactions include products
only when evidence for their identity has been reported.
pH Effects:
The pH is quoted whenever it was given. In some cases rate constants
have been determined for particular ionic forms of the reactants.
When observed rate data over a pH range have been used to calculate k
for an individual
ionic form, that is noted in the comments.
The observed k may
be for a mixture of ionic forms of the substrate. When
the studies were carried out near the pK of a reactant and the contributions
of the individual species were not determined, the pK has been included in
the comments and the rate constant should be understood to be for a mixture
of reactant species. In some cases pK's given by the authors are included
in the comment, in other cases the pK's have been obtained from standard
reference works. Their only function is to indicate the
possible ionic forms of the substrate. The pK's quoted have not been evaluated by the
present authors.
Metal ions may also exist in a variety of forms due to hydrolysis.
When insufficient information is available the metal species have
been indicated only by their oxidation number (Stock number) and the species
could include one or more forms such as M(OH)xn+–, MOn+–,
MO2n+–,
etc., as well as polynuclear metal ions. Water molecules coordinated to metal
ions have been omitted, e.g. Cr2+ is listed not Cr(H2O)62+, but
coordinated hydroxide ions and other anions are included, e.g. FeOH2+,
ThSO42+, etc.
Rate Constants:
Rate constants have been rounded to one or two significant figures and author's
error limits have been omitted.
For certain reactions a selected value is listed and those values have been used to normalize relative
rate constants.
Other entries may include two or more values for which an
average value is listed.
No average has
been computed if the data were obtained under conditions (pH, ionic strength)
which were were substantially different. Furthermore, the average is omitted
if the values differ by more than a factor of two.
A few single values which are included are
not recommended because of deficiencies in the method and are so indicated.
Multiple values with a large discrepancy may also not be recommended
and are so indicated.
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