Robert E. Huie

THE REACTION OF NO WITH SUPEROXIDE

The rate constant for the reaction of NO with .O2- was determined to be (6.7 +/- 0.9) x 10(9) l mol-1 s-1, considerably higher than previously reported. Rate measurements were made from pH 5.6 to 12.5 both by monitoring the loss of .O2- and the formation of the product -OONO. The decay rate of -OONO, in the presence of 0.1 mol l-1 formate, ranges from 1.2 s-1 at pH 5 to about 0.2 s-1 in strong base, the latter value probably reflecting catalysis by formate.

Rate Constants for the Reactions of Atomic Oxygen (O 3P) with Organic Compounds in the Gas Phase

Rate constants for the reactions of atomic oxygen (O 3P) with organic compounds in the gas phase are compiled and critically evaluated. Data are given here as originally reported in the literature for a total of 107 organic reactants. From a critical evaluation of the data, recommended values for rate constants are given over specified temperature intervals, and where possible at 298 K and 1000 K. Estimated error limits are assigned to all recommended values.

Electron transfer reaction rates and equilibria of the carbonate and sulfate radical anions

Abstract Electron transfer reactions of the carbonate radical anion with azide, bromide, and hypochlorite ions have been studied by pulse radiolysis. From the equilibrium Br.-2 + CO2-3 ⇆ 2Br- + CO.-3 and the known redox potential for Br.-2/2Br- = 1.62V vs NHE we derive E = 1.59V for CO.-3/CO2-3. From this value and the equilibrium CO.-3 + ClO- ⇆ CO2-3 + ClO. we derive E = 1.41V for ClO./ClO-. The equilibrium reaction SO.-4 + Cl- ⇆ SO2-4 + Cl. was studied by laser photolysis, by using 248 nm excitation of S2O2-8 to produce SO.-4 and examining the rate of reaction of this radical with Cl- in the presence of varying concentrations of SO2-4. By modeling the reactions taking place in this system, we derive the rate constant for the reaction of Cl. with SO2-4 (2.5 × 108dm3mol-1s-1 at 0.1 mol dm-3 ionic strength), and from the known rate constant for reaction of SO.-4 with Cl- (4.7 × 108dm3mol-1s-1 at the same ionic strength) we derive the equilibrium constant. From the known redox potential for Clf.-2/Cl- = 2.41V we derive E = 2.43V for SO.-4/SO2-4.

The reaction kinetics of NO2(.).

The chemistry of NO2. is reviewed. Experimental results from both the liquid and gas phase, and from both aqueous and non-aqueous systems, are used to gain insight into the basic chemistry of this radical.

Rate constants for some oxidations of S(IV) by radicals in aqueous solutions

Abstract Rate constants were measured for several radical reactions important in the autoxidation of S(IV) in atmospheric droplets. For the reactions of the hydroxyl radical with sulfite and bisulfite, the rate constants were found to be 5.2 × 1010 and 4.5 × 109 M−1 s−1, respectively. For the reaction of the dichloride radical anion with bisulfite, a rate constant of 3.4 × 108M−1s−1 was obtained. The peroxysulfate radical was found to react with sulfite with a rate constant of 1.3 × 107M−1s−1, but only an upper limit of 3×105 could be derived for its reaction with bisulfite. In some cases, the rate constants are significantly different from those used previously in atmospheric models. The use of these results in a simple model suggests that secondary radical-radical reactions may be of considerable importance in the mechanism of sulfite autoxidation in the atmosphere.

Evanescent wave cavity ring-down spectroscopy with a total-internal-reflection minicavity

A miniature-cavity realization of the cavity ring-down concept, which permits extension of the technique to spectroscopy of surfaces, thin films, liquids, and, potentially, solids, is explored using a wave-optics model. The novel spectrometer design incorporates a monolithic, total-internal-reflection-ring cavity of regular polygonal geometry with at least one convex facet to induce stability. Evanescent waves generated by total-internal reflection probe absorption by matter in the vicinity of the cavity. Optical radiation enters or exits the resonator by photon tunneling, which permits precise control of input and output coupling. The broadband nature of total-internal reflection circumvents the narrow bandwidth restriction imposed by dielectric mirrors in conventional gas-phase cavity ring-down spectroscopy. Following a general discussion of design criteria, calculations are presented for square and octagonal cavity geometries that quantify intrinsic losses and reveal an optimal cavity size for each geo...

Chemical behavior of sulfur trioxide(1-) (SO3-) and sulfur pentoxide(1-) (SO5-) radicals in aqueous solutions

The chemistry of the radicals SO/sub 3//sup -/ and SO/sub 5//sup -/ has been investigated by using pulse radiolysis with kinetic spectrophotometry. Rate constants for the oxidation by SO/sub 3//sup -/ of a variety of organic compounds were measured and equilibrium constants determined for the reactions of SO/sub 3//sup -/ with chlorpromazine and phenol. SO/sub 3//sup -/ was found to be a mild oxidant with a redox potential of E(SO/sub 3//sup -//SO/sub 3//sup 2 -/) = 0.63 V (vs. NHE) at pH > 7 and E(SO/sub 3//sup -//HSO/sub 3//sup -/) = 0.84 V at pH 3.6. The reaction of SO/sub 3//sup -/ with O/sub 2/ was shown to produce SO/sub 5//sup -/. The oxidation of several compounds by SO/sub 5//sup -/ was found to occur more rapidly than their oxidation by SO/sub 3//sup -/. E(SO/sub 5//sup -//HSO/sub 5//sup -/) was estimated to be approximately 1.1 V at pH 7. 44 references, 2 figures, 2 tables.

Survey of Photochemical and Rate Data for Twenty‐eight Reactions of Interest in Atmospheric Chemistry

Photochemical and rate data have been evaluated for 28 gas phase reactions of interest for the chemistry of the stratosphere. The results are presented on data sheets, one per reaction. For each reaction, the available data are summarized. Where possible there is given a preferred value for the rate constant or, for the photochemical reactions, preferred values for primary quantum yields and optical absorption coefficients.

EVANESCENT WAVE CAVITY RING-DOWN SPECTROSCOPY FOR PROBING SURFACE PROCESSES

Abstract Sub-monolayer detection of adsorbed I 2 is demonstrated with the cavity ring-down technique by using intra-cavity total-internal reflection to generate an evanescent field that probes the adsorption process. A precision, fused-silica Pellin-Broca prism with ultra-smooth facets (surface roughness ∼0.05 nm r.m.s) is employed to provide the intra-cavity TIR. The known cross-section for the 1 Σ g + → 3 Π u transition of I 2 , which is largely invariant between pressure-broadened gaseous, weakly chemisorbed, and liquid states, provides quantification of sensitivity. A minimum detectable coverage of ∼0.04 monolayer is determined at a weakly absorbed probe wavelength.

Rate constant for the reaction of nitrogen dioxide with sulfur(IV) over the pH range 5.3-13.

Rate constants have been determined for the reactions of NO{sub 2} with SO{sub 3}{sup 2{minus}} and HSO{sub 3}{sup {minus}} in aqueous solutions. A pulse radiolysis apparatus with signal averaging, which has allowed us to monitor the decay of NO{sub 2} directly and to measure rate constants for the reaction of NO{sub 2} with SO{sub 3}{sup 2{minus}} and HSO{sub 3}{sup {minus}} over the pH range 5.3-13. The rate constant increases from about 1.2 {times} 10{sup 7} M{sup {minus}1} s{sup {minus}1} near pH 5 to 2.9 {times} 10{sup 7} M{sup {minus}1} s{sup {minus}1} at pH 13. The reaction appears to involve the formation of an intermediate complex that may undergo subsequent reaction with NO{sub 2} to yield the ultimate products or may react with other substrates present. The formation of a long-lived intermediate would have implications on the chemistry of flue gas scrubbers and on luminol-based NO{sub 2} detectors.