Exploring the Reactions of Fe+ and FeO+ with NO and NO2

We report for the first time temperature dependences (from 300 to 600 K) of the reactions of Fe+ and FeO+ with NO and NO2. Both ions react quickly with NO2, and their rate constants have weak negative temperature dependences. The former is consistent with the calculated energy profile along the Fe+ + NO2 reaction coordinate. Ground state Fe+ reacts with NO2 to produce only FeO+, while FeO+ reacts with NO2 to produce NO+ exclusively. Certain source conditions produce excited Fe, as evidenced by production of primary NO, which is endothermic with the ground state by 0.35 eV. The room temperature rate constants are in agreement with previous values. For the reactions of Fe+ and FeO+ with NO, we find an upper limit of < 1.0 x 10(-12) cm(3) s(-1) for both rate constants, in contrast to a previous report of a rate constant of similar to 1.7 X 10(-11) cm(3) s(-1) for Fe+ + NO. Because this is an endothermic process, the prior report interpreted the reaction as a termolecular process involving two NO molecules; instead, we show that the previous results were likely due to an NO2 impurity. Implications for other metal cation reactions which have been speculated to occur by the termolecular mechanism are discussed.