Interpretation of the Data on the Thermal Decomposition of Nitrous Oxide

Abstract

The data on the thermal decomposition of nitrous oxide, which as they stand are anomalous in many respects, are examined. It is found at low concentrations of nitrous oxide that a heterogeneous first-order reaction of low energy of activation becomes important. Correction of all data for this heterogeneous reaction removes most of the anomalous spread of values of the energy of activation which had varied from 48 to 65 kcal per mole. The energy of activation at the low concentration limit is 59 kcal per mole, which gives normal pre-exponential factors and ``number of oscillators.'' The data, corrected for heterogeneity, are those for a straightforward unimolecular reaction, giving the low concentration limit and approaching the high concentration limit. By empirical modification of existing theories specific rate constants are found for the variously excited molecules which give a good description of the observed curve of log rate-constant vs log-concentration. The function of specific rate constants vs energy of the molecule is closely related to the continuous form proposed by Rice and Ramsperger, who assume four effective oscillators, which is the number of normal modes of vibration of the nitrous oxide molecule. More experimental work is needed on this kinetic system.