Direct Observation of the Thermal Dissociation of Molecular Nitrogen

Published experiments on the thermal dissociation of N2 generally report a failure to detect it. These negative results were helpful in deciding between the two possible values 9.765 and 7.385 eV for the dissociation energy, proposed by band spectroscopists, because the experiments should have detected dissociation if the lower energy were correct. Our experiments performed with a mass spectrometer employed a tungsten ribbon as a catalyst. This was mounted adjacent to the ionization chamber. The observed rate of dissociation, in the range 2450–2800°K, was only consistent with the larger dissociation energy. As in reactions previously studied by this technique, the rate-limiting step appears to occur inside the catalyst, rather than on its surface. However, the high temperatures required for measurable dissociation prevented a detailed examination, so that one cannot be as confident of a volume process as for past tests. Our measurements have relevance for processes proposed by others which had not previously been re-examined.