Modeling of nitrogen atom recombination on Pyrex: Influence of the vibrationally excited N2 molecules on the loss probability of N

Abstract

A numerical modeling of the surface recombination of nitrogen atoms on Pyrex is developed to account for the temperature dependence of the loss probability γ on the temperature in the range 290–611.5 K. Nitrogen atom recombination is a first-order Langmuir–Hinshelwood mechanism at a temperature below 400 K where both the Langmuir–Hinshelwood and the Eley–Rideal mechanisms are taking place above. Calculated results are compared to experimental measurements obtained in an Ar–N2 Lewis–Rayleigh afterglow. Satisfactory agreement is obtained. The activation energy of the recombination processes is close to 20 kJ/mol. The weak difference between the theory and the experiment is due to the value of the model parameters and not to the influence of the vibrationally excited molecules, which is very weak. It is suggested that the rate constant for vibrational de-excitation of N2(X,v) by an adsorption–phonon mechanism is underestimated. The recombination rate of nitrogen atom on the wall of a cylindrical Pyrex tube is described by d[N]/dt|vsurfaceprocesses=−k[N], with k=γc̄N/2R. The temperature dependence of γ is provided and it is complex but a rough estimation of the rate constant is given by k=17.9 exp(−5900/RT), with T in the range 290–611.5 K.