Absolute rate coefficients for the reactions of O2−+N(S3∕24) and O2−+O(P3) at 298 K in a selected-ion flow tube instrument

The absolute rate coefficients at 298 K for the reactions of O(2) (-) + N((4)S(3/2)) and O(2) (-) + O((3)P) have been determined in a selected-ion flow tube instrument. O atoms are generated by the quantitative titration of N atoms with NO, where the N atoms are produced by microwave discharge on N(2). The experimental procedure allows for the determination of rate constants for the reaction of the reactant ion with N((4)S(3/2)) and O((3)P). The rate coefficient for O(2) (-) + N is found to be 2.3x10(-10)+/-40% cm(3) molecule(-1) s(-1), a factor of 2 slower than previously determined. In addition, it was found that the reaction proceeds by two different reaction channels to give (1) NO(2)+e(-) and (2) O(-)+NO. The second channel was not reported in the previous study and accounts for ca. 35% of the reaction. An overall rate coefficient of 3.9 x 10(-10) cm(3) molecule(-1) s(-1) was determined for O(2) (-) + O, which is slightly faster than previously reported. Branching ratios for this reaction were determined to be <55%O(3) + e(-) and >45%O(-) + O(2).