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Issue 30, 2017
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Trapping-desorption and direct-scattering of formaldehyde at Au(111)

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Nonreactive surface scattering of atoms, molecules and clusters can be almost universally described by two mechanisms: trapping-desorption and direct-scattering. A hard cube model with an attractive square well provides a zeroth order description of the branching ratio between these two mechanisms as a function of the incidence energy. However, the trapping process is likely to be enhanced by excitation of internal degrees of freedom during the collision. In this molecular beam surface scattering study, we characterize formaldehyde/Au(111) scattering using angle resolved time-of-flight techniques. The two mechanisms are found to compete in the range of the investigated normal incidence energies between 0.1 and 1.3 eV. Whereas at low incidence energies trapping-desorption dominates, direct-scattering becomes more likely at incidence energies above 0.37 eV. This incidence energy is slightly higher than the desorption energy which is found to be 0.32 ± 0.03 eV by temperature programmed desorption techniques. A simple hard cube model underestimates the observed trapping probabilities indicating the importance of trapping induced by excitation of internal molecular degrees of freedom.

Graphical abstract: Trapping-desorption and direct-scattering of formaldehyde at Au(111)

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Publication details

The article was received on 12 Jun 2017, accepted on 09 Jul 2017 and first published on 10 Jul 2017

Article type: Paper
DOI: 10.1039/C7CP03907G
Citation: Phys. Chem. Chem. Phys., 2017,19, 19896-19903
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    Trapping-desorption and direct-scattering of formaldehyde at Au(111)

    B. C. Krüger, G. B. Park, S. Meyer, R. J. V. Wagner, A. M. Wodtke and T. Schäfer, Phys. Chem. Chem. Phys., 2017, 19, 19896
    DOI: 10.1039/C7CP03907G

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