I. K. Larin

Experimental Evidence for Acceleration of Reaction between Iodine Monoxide and Chlorine Monoxide at the Reactor Surface

The reaction of iodine monoxide with chlorine monoxide resulting in atom escape to the gas phase is studied at T = (303 ± 5) K and P = 2.5 Torr using a flow setup for measuring the resonance fluorescence signals of atomic iodine and chlorine. The heterogeneous reaction between chlorine monoxide and iodine monoxide occurring at the reactor surface covered with an F32-L Teflon-like compound and treated by the reaction products is characterized by the rate constant k = (4.9 ± 0.2) × 10–11 cm3 molecule–1 s–1. This value is substantially higher than the rate constant for the homogeneous reaction IO· + ClO· (k1 ≤ 1 × 10–12 cm3 molecule–1 s–1).

Iron Catalysis of SO2 Oxidation in the Atmosphere

The mechanisms of SO2 oxidation catalyzed by iron ions in the droplet phase of the convective cloud in the lower atmosphere were examined. The relations of the catalytic SO2 decrease to the concentration of the iron ions and to the intensity of fluxes to the droplet of the OH•(g) and HO•2(g) radicals were characterized. The determining role of the replacement of the low-reactive HO•2(g)(O–•2(aq)) radical by the reactive SO–•5(aq) radical in the sulfite medium during daytime was revealed. This process occurred due to the coupling of the decay of the radicals and their regeneration in the liquid-phase reactions O–•2(aq) + FeOH2+(aq) → Fe2+(aq) + OH–(aq) + O2(aq) , HSO–5(aq) + Fe2+(aq) → FeOH2+(aq) + SO–•4(aq)HSO3-(aq),O2(aq) SO–•5(aq).

Increase in the apparent rate constant of the reaction of hydrogen sulfide with ozone upon the treatment of the reactor surface with reaction products

The reaction of hydrogen sulfide with ozone at 343 K was studied in a flow reactor whose inner surface was coated with 32-L fluoroplastic both immediately after coating and after repeatedly treating with reaction products (sulfur compounds). In the latter case, the rate of hydrogen sulfide reaction with ozone increased by more than one order of magnitude.

Kinetics and mechanism of CH3Br, CHF2Br, and C2HF4Br photolysis in the presence of dioxygen under the action of λ = 253.7 nm light

The photolysis of CH3Br, CHF2Br, and C2HF4Br mixed with oxygen under radiation emitted by a bactericidal mercury lamp (radiation intensity maximum at λ = 253.7 nm) has been investigated. Oxygen was added in order to simulate natural conditions. A photolysis mechanism has been suggested, the corresponding model calculations have been carried out, and the calculated data have been compared with experimental data. The calculated absorption cross sections are in agreement with the literature, thus proving the validity of the mechanism suggested. The ratios between the rate constants of the reactions of the photolytically generated CH3, CHF2, and C2HF4 radicals with molecular bromine and oxygen have been determined.

Formation of iodine atoms in the heterogeneous reaction between chlorine and iodomethane

The rate constant of the reaction between iodomethane and chlorine atoms at 323 K, measured by the resonance florescence method under jet stream conditions as the iodine atom yield, is k1I = (2.9±0.6) × 10−12 cm3 molecule−1 s−1. It is demonstrated experimentally that this reaction takes place mainly on the reactor wall.

Mechanism and kinetics of the reaction between hydrogen iodide and ozone

The reaction between hydrogen iodide and ozone at 295 K has been investigated by the resonance fluorescence method applied to the detection of iodine atoms. A chain mechanism is suggested for this reaction. The chain initiation rate constant is k1 = (5.45 ± 1.80) × 10−17 cm3/s, and the chain propagation rate constant is k3 = (1.1 ± 0.4) × 10−12 cm3/s.

Drop size effect on the rate and mechanism of SO2 oxidation in tropospheric clouds

The drop size effect on the rate and mechanism of sulfur dioxide oxidation in tropospheric clouds is analyzed. In the daytime, the oxidation rate decreases as the drops grow. This effect is due to the fact that the liquid-phase reactions slow down because of a decreasing influx of oxidizing species, namely, H2O2, OH., HO.2, and O3. The effect of the nonuniformity of OH. and O3 distribution in the drop bulk on the reaction rate is discovered.

Measuring the rate constant of the reaction between carbon monoxide and iodine oxide at 298–363 K by the resonance fluorescence method

The rate constant of the reaction between the IO radical and carbon monoxide has been measured by the iodine atom resonance fluorescence method in the temperature range from 298 to 363 K. The reaction mainly takes place on the wall of the reactor.

Kinetics and mechanism of the photodecomposition of trifluorobromomethane and tetrafluorodibromoethane under the action of light with a wavelength of 253.7 nm

The kinetics of photodecomposition of Halons CF3Br and C2F4Br2 was studied at different times of the irradiation of a mixture of these substances with oxygen at the wavelength λ = 253.7 nm. Kinetic data were obtained from changes in the absorption spectra in the region of Halon absorption and at a wavelength of 416 nm, which corresponds to the absorption maximum of molecular bromine. Kinetic schemes were proposed for the photodecomposition of CF3Br and C2F4Br2 at λ = 253.7 nm, and the quantum yields of their photodecomposition at this wavelength were determined.

Measurement of the reaction rate constants of oxygen atoms with chlorine and iodomethane using a resonance fluorescence technique

The following reaction rate constants of oxygen atoms with iodomethane and chlorine were measured using resonance fluorescence under jet conditions at 298 K: k1 = (2.4 ± 0.5) × 10–15 and k2 = (6.9 ± 0.2) × 10−14 cm3/s, respectively.