THE KINETICS OF THE DECAY OF NITROGEN ATOMS AS DETERMINED FROM CHEMICAL MEASUREMENTS OF ATOM CONCENTRATIONS AS A FUNCTION OF PRESSURE

Abstract

A method is described for studying both the surface and homogeneous decay of N atoms in which the atom concentration reaching a reaction vessel after a period of decay is measured as a function of pressure by HCN production from ethylene or ethane under conditions of complete consumption of the atoms and complete initial dissociation of the nitrogen. The results indicated that the surface decay proceeded by a first-order mechanism between 55 °C and 400 °C, with the collision efficiency for an Na₂HPO₄ surface essentially constant at 2.75 × 10⁻⁴. The activation energy of surface decay was 1.0 kcal mole⁻¹ and the concentration of surface species 1.9 × 10¹⁴ cm⁻². It was concluded that the surface decay probably leads directly to molecules in the ground state.Depending on the temperature and whether or not N₂ and N were considered equivalent as third bodies, the rate constant of the homogeneous decay varied from 1.09 × 10⁻³³ to 13.2 × 10⁻³³ cc² molecule⁻² sec⁻¹. The homogeneous decay therefore appears to have a positive temperature coefficient and to be of only secondary importance below about 2 mm pressure under the prevailing conditions. The similarity of one-half the rate constant of homogeneous decay at 25 °C (0.55 × 10⁻³³ to 0.97 × 10⁻³³) to the rate constant of afterglow emission obtained by Berkowitz etal. (2 × 10⁻³³) suggests that all homogeneous decay gives rise to afterglow via the ⁵Σ state.