Kinetics of Desorption of the β-Nitrogen States Chemisorbed on Tungsten
- 15 February 1966
- journal article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 44 (4), 1675-1684
- https://doi.org/10.1063/1.1726908
Abstract
The kinetics of desorption of the strongly chemisorbed β1 and β2 nitrogen states on tungsten have been studied. Independent techniques of isotopic mixing and flash-filament desorption have been employed. The rate of production of 14N15N (g) from 14N2(g) and 15N2(g) in a steady-state flow experiment is completely accounted for by the kinetically determined rate of desorption from the chemisorbed layer. β1-nitrogen appears to desorb by first-order kinetics; β2-nitrogen desorbs in a complex manner with higher-order kinetics. The apparent β2 desorption order decreases markedly as temperature increases. A superposition of two or more unresolved substates in the β2 state is postulated. The temperature variation of desorption order can be accounted for by a lack of achievement of equilibrium between the spatially separate β2 substates during desorption at scan rates of 12.5°K/sec or greater. Above 1500°K, where the steady-state coverage of nitrogen is very low, a sticking coefficient of less than 0.02 has been measured. The sticking coefficient is nearly constant in the range 1500°—1700°K and over a 25-fold pressure range.Keywords
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