Interaction of diatomic molecules with clean metal wire surfaces. Part 2.—Nitrogen on tungsten

Abstract

Heats of adsorption, sticking probabilities and temperature programmed desorption spectra are reported for nitrogen on polycrystalline tungsten at 290 and 222 K. The initial heat of adsorption at 290 K was found to be 380 ± 14 kJ mol^–1. Three atomic states for nitrogen adsorption on tungsten were found to desorb between 1150 and 1450 K. In addition, a metastable, molecular state of nitrogen was found which desorbed between 200 and 950 K. This metastable state, able to cover an estimated 10 % of the surface at 222 K, was found to dominate the adsorption behaviour of nitrogen on tungsten at 222 K. It had an estimated heat of adsorption of 190 kJ mol^–1. The ability to investigate such metastable states is an important feature of the calorimetric technique which has been employed.