Mechanism of thermal electron attachment in N2O–CO2 mixtures in the gas phase

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Abstract
The attachment of thermal electrons to nitrous oxide in N2O–CO2 mixtures has been studied at room temperature in the pressure range 5–120 torr. Ionization was by pulse radiolysis and the electron concentration was measured as a function of time by microwave conductivity. Addition of even less than 0.1% CO2 to N2O causes a marked increase in attachment rate. However, this enhancement soon saturates in that further additions of CO2 have less and less effect. Experiments with ternary mixtures including C2H6 showed a further enhancement which was much larger than the additive effects of CO2 and C2H6 alone. These observations can be explained by a two step three‐body process producing vibrationally excited N2O−* if the rate constant for stabilization of N2O−* by CO2 is 4×10−30 cm6/molecule2⋅sec. The decrease in effectiveness with increased CO2 pressure is interpreted as the collisional ionization of a complex ion, [N2O⋅CO2]−*. The nonadditive effect of hydrocarbon results from the rapid reactive destruction of such complexes by collision with the hydrocarbon. A detailed quantitative treatment of the proposed mechanism was successful in explaining most features of the data. In a limited set of experiments, allene —N2O mixtures were found to behave much like CO2–N2O.

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