The Kinetics of the thermal oxidation of NO in solid oxygen between 13 and 29 K; direct observation of the reaction of (NO)2 and oxygen

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Abstract
The kinetics of the reaction of cis‐(NO)2 with solid oxygen to form iso‐N2O4 have been studied between 13 and 29 K. The overall reaction is pseudo first order in cis‐(NO)2, and solid oxygen serves both as a reactant and the matrix. The pseudo‐first‐order rate constants are calculated to be k(14N) = 4.25 × 10−2 exp(‐103/RT), and k(15N) = 3.00 × 10−2 exp(‐105/RT) sec−1, based on temperature measurements from a thermocouple junction which may be at most three degrees lower than the actual reacting film. Most significantly, however, 14k/15k = 1.55 at∼13 K. The condensed phase reaction has been compared to that observed in the gas phase, and the extremely small pre‐exponential factors and large isotope effects have been discussed in terms of tunneling corrections and orientational constraints. It is suggested that the form of the crystal plays an integral role in the observed process.
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