The laser photolytic production of the IO radical from N20/Iz/N2 mixtures was used to measure the radical absorption spectrum from 340 to 450 nm. Two new absorption peaks at 403 and 411 nm were observed along with an underlying continuum starting at about 420 nm and extending to about 350 nm. An absorption cross section of (2.8 f 0.5) x cm2, in good agreement with previous measurements, was determined for the (4-0) band head at 427.2 nm. From the rate of formation of IO and the rate of loss of 12, rate constants for the reactions 0 + I 2 -IO + I and 0 + IO -0 2 + I of (1.4 f 0.4) x and (1.2 f 0.5)x cm3 s-l, respectively, were derived. Finally, from the rate of decay of IO, a rate constant for the reaction IO + IO -products of (8.0 =t 1.8) x lo-" cm3 s-l was obtained. All of the uncertainties expressed are 2 standard deviations derived from the statistical analysis and do not include estimates for possible systematic errors.
The reaction of NH3 with •OH or SO4
•- radicals produces the aminyl radical, •NH2. Pulse radiolysis and
laser flash photolysis techniques were utilized to study the formation of this radical, its absorption spectrum,
its reaction with O2, and the mechanism of formation of subsequent intermediates and the main final product,
peroxynitrite. The rates of formation of •NH2 and its absorption spectrum are in agreement with previous
reports. The reaction of •NH2 with O2, however, was observed to take place much more rapidly than reported
before and to involve an equilibrium of these reactants with the aminylperoxyl radical, NH2O2
•. The equilibrium
is shifted toward completion of the reaction via catalyzed decomposition of this peroxyl radical, and this
decomposition affects the observed rate of reaction of •NH2 with O2. The peroxyl radical deprotonates and
isomerizes and finally forms NO. In the presence of O2
•-, NO is converted rapidly to peroxynitrite, ONO2
-.
This product, which is stable at alkaline pH, was confirmed by γ-radiolysis of aerated ammonia solutions.
Benzophenone – isopropyl alcohol – acetonitrile, benzophenone – benzhydrol – acetonitrile and acetone – isopropyl alcohol – acetonitrile systems were studied by laser flash photolysis transient absorption technique and by steady‐state quantum yield determinations. Kinetic parameters were derived for reactions of the ketyl radicals formed in the primary photoreduction steps. The room temperature overall rate coefficients at 0.001 mol dm−3 benzophenone and 2.6 mol dm−3 isopropyl alcohol in acetonitrile are in 108 dm3 mol−1 s−1 units: 12.8 ± 0.6, 8.0 ± 0.4 and 0.59 ± 0.01 for Mc2ĊOH + Me2ĊOH, Me2ĊOH + Ph2ĊOH and Ph2ĊOH + Ph2ĊOH, respectively. (The error limits represent 2 standard deviations.) Combination was shown to be the only significant reaction in the interaction of two Ph2ĊOH radicals, while disproportionation is the dominating path in the reactions inolving Me2ĊOH radicals. Evidences are presented for the existence of four reaction channels in the cross reaction of the two ketyl radicals. These are combination (4a), disproportionations (4b) and (4c) and formation of a “light absorbing transient” (4d), with branching ratios k4a/k4 = 0.18 ± 0.08, k4b/k4 = 0.61 ± 0.11, k4c/k4 = 0.05 ± 0.02 and k4d/k4 = 0.18 ± 0.03, respectively. – The radical transfer reaction Me2ĊOH + Ph2CO → Me2CO + Ph2ĊOH, which may change considerably the product distribution and quantum yields in the photoreduction of benzophenone by isopropyl alcohol at medium and low light intensities, was investigated by quantum yield determinations and a room temperature rate coefficient of k5 = (7.3 ± 1.2) · 104 dm3 mol−1 s−1 was extracted through computer model simulation. This rate coefficient is considerably lower than the values reported previously.
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