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A mass-spectrometric stirred-reactor technique was used t o study the reaction of atomic oxygen with methane with low concentrations of molecular oxygen. An overall rate constant for oxygen-atom disappearance due t o added methane was obtained for the temperature range 375 to 576 OK. This rate constant was 4 X 1014 exp (-10 000/RT) cm3 m~l e -~s -l and was compared with a previous rate constant for this reaction that had been measured in the presence of a large excess of molecular oxygen. This comparison showed that the presence of a n excess of molecular oxygen produced a considerable increase in oxygen-atom consumption a t low temperatures, but only a small increase a t high temperatures. From product analyses, the stoichiometry of the reaction could be approximately represented by From the reaction stoichiornetry and the rate constant for the oxygen-atom disappearance, the rate constant for methane disappearance was calculated t o be 1 X 1014 exp (-10 000/RT) cm3 mole-' s-'. The presence of excess molecular oxygen has very little effect on this rate constant, contrary to the result found for the disappearance of atomic oxygen.

Calculation of the rate constant for the reaction of atomic hydrogen with molecular oxygen to form the free radical HO2 J. Chem. Phys. 73, 765 (1980); 10.1063/1.440182 Product distributions and rate constants for ionmolecule reactions in water, hydrogen sulfide, ammonia, and methaneThe stirred-reactor technique was used to measure the reaction rates of H2, NH3, and CH, with mixtures of atomic and molecular oxygen (0+02) at temperatures ranging from 350° to 6OO 0 K. A mass spectrometer capable of detecting atomic oxygen and hydrogen was used to analyze the reacting mixture in the stirred reactor. It was discovered that atomic oxygen could be quantitatively monitored by the mass spectrometer at a mass-to-charge ratio of 8. The reaction of H2 with the 0+02 mixture was found to be a chain reaction, with four to six atoms of oxygen consumed for each hydrogen molecule. The rate constant for the disappearance of atomic oxygen was 3XlO '3 exp(-8300/RT) ccmole-lsec l . The products of the reaction were H20 and H. The reactions of NH3 and CH, with the 0+02 mixture were complex chain reactions, with a minimum of eight atoms of oxygen disappearing for each molecule of NH3 or CH,. Rate constants for atomic-oxygen disappearance were 3 X 10'2 exp ( -4800/ RT) cc mole-l secl and 2 X 10'3 exp ( -6900/ RT) cc mole-l sec-l, respectively. The products of the former reaction were NO, H20, and small amounts of H2 and H. The products of the latter reaction were H20, CO2, and small amounts of CO, H2, and H.

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