A wide-temperature-range, fast-flow reactor with esr detection has been used to measure the rate coefficient for the reaction 0 + C2H2 + CO + CH2 over the range 195-616°K. Values of k1 at room temperature are in good agreement with previous results. The Arrhenius plot of kl is curved, but in the region 230-450°K where the plot is approximately linear the expression kl = 2.0 X 1013 exp(-3200/RT) cm3 mol-' sec-' is obeyed. Stoichiometric measurements by combined esr and mass spectroscopy with C2H2 in excess show that two 0 atoms are consumed per C2H2 independent of temperature. The reaction mechanism is discussed and compared with 0 + CzH4, revealing some interesting similarities and differences. The moderately pronounced temperature dependence of kl found in this work may be significant for the interpretation of other high-temperature results in flames and shock waves.

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The rate of the O + SO3 reaction has been measured under pseudo−first−order conditions in a discharge flow reactor with ESR detection. The reaction is shown to be a fast third−order process at pressures up to 7 torr, a fact not brought out in previous work. Third−order rate constants obtained for M = He at 298, 385, and 507°K are 7.3±0.2, 3.8±0.2, and 2.4±0.2×1017 cm6 mole−2⋅sec−1, respectively, the data obeying k = 5.0×1016 exp(785/T) in this range. At 298°K, the ratio k (M = N2)/k (M = He) is 1.4, and it is shown that the ratio k (M = SO3)/k (M = He) probably cannot be greater than about 10. The reaction products are written as SO2 + O2, no evidence being found for a stable SO4 in the gas phase. Analogous measurements on N + SO3 indicate it is too slow to measure by this technique (bimolecular rate constant <6×106 cm3 mole−1⋅sec−1), in disagreement with other reported results.

The general theory relating the measured integrated intensities of ESR absorption lines to the concentrations of odd electron species in the gas phase is reviewed and discussed in some detail. It is then applied in the form required for determining the absolute concentrations of O, N, and H atoms using O2 as a calibrating gas as first suggested by Krongelb and Strandberg. Experimental data are presented which verify the theoretical predictions of the intensities of various O2 lines. The determination of absolute O and N concentrations by ESR is shown to be a reliable experimental technique by comparison with the independent results of titration with NO2 and NO, respectively. Agreement of the two techniques strongly supports the validity of both. The O–NO2 titration curves enable a value for the rate constant of O+NO+O2→ lim k6NO2+O2to be evaluated at 300°K as 2.9×1016 cm6 mole—2 sec—1 in agreement with other reported values.

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