Field ionization of Rydberg alkali states outside iron oxide catalyst surfaces: peaked angular distributions of ions

Åman, Carina; Holmlid, Leif

doi:10.1016/0169-4332(93)90022-4

Cited by 21 publications

(22 citation statements)

References 16 publications

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“…Strong interaction between the flux from the beam and the thermally desorbing flux from the surface is also reported, such that peaks observed without an impinging atom beam are removed by the beam flux. These observations are related to the existence of excited clusters K* identified in previous studies [1][2][3][4]10]. The results demonstrate the importance of scattering studies to investigate the nature of the excited species at catalyst surfaces.…”

Section: Introductionsupporting

confidence: 67%

“…displaying lobes in the normal direction for neutral desorption [2,10], as well as peaks at large angles from the normal 1-2, 3,10] for the ionic signal. The interpretation in these cases involves cluster formation outside the sample for the peaks in the normal direction for the neutral flux, and probably cluster desorption, fragmentation and ionization in the external electric field just outside the sample in the case of the ionic peaks at large angles from the normal.…”

Section: Properties Of Rydberg Speciesmentioning

confidence: 99%

“…The most efficient sources of small electronically excited clusters found so far are alkali promoted catalysts of the type used in the present study. The collisional properties of such clusters have not been studied before, even if experiments with cluster formation have been published [2, 3,10,20]. The possible potential energy surfaces describing the interaction between a ground state K atom and an.…”

Section: Properties Of Rydberg Speciesmentioning

confidence: 99%

“…A surface scattering behavior of potassium atom beams has also recently been observed [2,3] from the same kind of surfaces. The surfaces used were cut flat from pellets of an industrial catalyst, the potassium promoted iron oxide catalyst for styrene production, but the surfaces used are still very rough.…”

Section: Introductionmentioning

confidence: 95%

“…Angular distributions of desorbing potassium neutrals and ions from special surfaces have been shown [1][2][3][4] to depart strongly from the expected equilibrium cosine-type distributions. A surface scattering behavior of potassium atom beams has also recently been observed [2,3] from the same kind of surfaces.…”

Section: Introductionmentioning

confidence: 99%

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Scattering of a potassium atom beam from potassium promoted catalyst surfaces via electronically excited clusters

Holmlid

1995

Z Phys D - Atoms, Molecules and Clusters

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Abstract. Surface scattering of potassium atom beams is observed from surfaces of a potassium promoted catalyst, which is known to emit Rydberg K* species and clusters K*. The surfaces studied are cut flat from pellets of an industrial catalyst, the promoted iron oxide catalyst for styrene production. The scattering is studied in the temperature range 500-1000 K in an UHV apparatus with a K atom beam at 45 ° towards the normal, with surface ionization and ion detection over an angular range of -90 ° to + 90 ° with respect to the surface normal. Bilobular scattering patterns are observed, which are mainly back-scattering at low temperatures, below 750 K. A large signal due to ions emitted in the backwards direction is also found with a voltage on the sample. This back-scattering indicates that the scatterers are heavy clusters outside the surface. The ion formation in the backwards direction is proposed to be due to collisions with electronically excited clusters K* of the type recently observed by field ionization detection (Kotarba et al. 1994). The bilobular scattering transforms into asymmetric patterns with a larger forward (specular) lobe at higher temperatures, above 800 K. Only a small fraction of the beam molecules is scattered off the surface. The scattering is well described by inelastic surface scattering theory. This shows that the actual scattering surface is rather flat, which is proposed to be due to an antibondii~g Rydberg type interaction, of long range (hundreds of A), between the impinging excited K atom and the surface. The temperature dependence of the neutral scattering gives a barrier of 0.96 eV, close to what is generally found for Rydberg species emission from such surfaces. At larger K s~r-face densities, the contributions to the peaks from the beam flux is shown to agree with this picture involving collisions with excited clusters outside the surface.

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Section: Introductionsupporting

confidence: 67%

Section: Properties Of Rydberg Speciesmentioning

confidence: 99%