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Desorption rates and mechanisms for dissociatively chemisorbed molecules

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Abstract

The desorption kinetics of dissociatively chemisorbed diatomic molecules are examined from a kinetic-modeling point of view. A comparison is made between a one-step process, resulting in the usual second-order kinetics, and a two-step process which takes into account explicity recombination of atoms and subsequent desorption of molecules. The kinetics from the two-step mechanism are found to be equivalent to second-order desorption with a coverage-dependent activation energy which, in many cases, is a linear function of coverage. The two-step process leads to second-order kinetics with a constant activation energy only for special values of the model rate parameters, or if chemisorption is activated. The steady onate approximation for the intermediate in the two-step process is often adequate, but the transient period during which a steady state is reached also contains important kinetic information. The implications of these results for desorption kinetics and molecular beam reaction experiments are discussed.

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Work performed under the auspices of the Office of Basic Energy Sciences of the Department of Energy

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Steinbrüchel, C. Desorption rates and mechanisms for dissociatively chemisorbed molecules. Appl. Phys. 19, 413–420 (1979). https://doi.org/10.1007/BF00930105

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PACS

  • 82.65