AVS 45th International Symposium
    Vacuum Technology Division Tuesday Sessions
       Session VT-TuM

Paper VT-TuM4
Measurements Illustrating the Importance of Desorption and Molecular Residence Times on the Molecular Drag Process

Tuesday, November 3, 1998, 9:20 am, Room 329

Session: Molecular Drag Pumping
Presenter: A.D. Chew, BOC Edwards, United Kingdom
Authors: A.D. Chew, BOC Edwards, United Kingdom
R.A. Abreu, BOC Edwards, United Kingdom
I. Creaye, BOC Edwards, United Kingdom
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Knowledge of the molecular residence time is a fundamental factor in the understanding of molecule-surface interactions and has special relevance in the analysis of the molecular drag process. In this paper we describe experiments based on a technique originally devised by Holst and Clausing.@footnote 1@ In this technique molecules are beamed onto a variable high speed rotating disc and the point of desorption is measured. This in principle provides a means for the direct determination of the residence time. Preliminary results for various gas-surface combinations including nitrogen, helium, oxygen, krypton and perfluorocarbons on aluminium are presented. The method was further exploited to investigate the effect of surface speed on the desorption flux distribution, and to give insight into the mechanism of the molecular drag process for gases of different molecular mass. The possible application of this phenomenon to gas separation is discussed. @FootnoteText@ @footnote 1@G Holst and P Clausing, Physica 6, 48 (1926)