lamp intensity profile also at each time step. After trials
involving smaller time increments were found to give
identical results, the time interval was chosen to be 0.25 s.
All of the data used for the simulations are collected in
Table 3.
on the square of the light intensity, both of these details
lead to higher real rates of radical-radical reactions than
in our simulation. In order to agree with experiment, the
simulation must compensate by using a much larger
assumed value for the associated rate constant (reaction
25).
Kinetic simulations, in general, are independent of many
of the details of the proposed reaction scheme. Thus, for
instance, the exact sequence ofreactions leading from acetic
acid to oxalic acid is irrelevant as long as no stable
intermediates are formed and no intermediates couple this
reaction to others outside the acetic acid/ oxalic acid “black
box”. On the other hand, the photolysis of hydrogen
peroxide is an example where the details are relevant, since
the hydroxyl radicals couple this reaction to many others.
Simulations of the photolysis of hydrogen peroxide in
the absence of acetone involved the reactions 1-4 as well
as reactions 40 and 41 in Table 3. Reaction 41 is a chain
propagation step that results in a quantum yield for
hydrogen peroxide destruction greater than one under low
light flux conditions. By contrast, reaction 40 results in a
quantum yield less than one for very high light intensities.
Under our conditions, these latter two reactions had a
negligible effect. As discussed previously, this entire set of
reactions gives a quantum yield of unity for hydrogen
peroxide destruction. However, our experimental results
could only be fit if the quantity φOHGo was reduced to 80%
of its expected value. Either the primary quantum yield for
hydroxyl radical production had to be reduced to 0.80 or,
if the literature value of 1.0 is accepted, the value for Go is
only 80% of that measured by actinometry. The value for
φOHGo measured in our experiments on hydrogen peroxide
photolysis was used in our acetone simulations.
Acknowledgments
This work was supported financially by a Collaborative
Research and Development Grant jointly funded by the
Natural Sciences and Engineering Research Council of
Canada and Solarchem EnvironmentalSystems ofMarkham
Ontario, Canada. We thank Dr. Stephen Cater, Dr. Ali
Safarzadeh-Amiri, Mr. Keith Bircher, P. Eng, and Dr. R. D.
Samuel Stevens of Solarchem Environmental Systems for
their helpful comments and support during the conduct of
this research.
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