Robson, R. E.Petrović, Z. Lj.Raspopović, Z. M.Loffhagen, D.2015-10-082015-10-080021-9606http://hdl.handle.net/1885/15810A number of recent theoretical investigations of electron motion in attaching gases demonstrate the possibility of a steady-state situation in which the electric current opposes the applied field. This phenomenon, which has been called “negative absolute electron mobility”, implies a Joule cooling effect and an associated negative entropy production, suggesting, at first glance, a possible violation of the second law of thermodynamics. In this article we show that the entropy production has in fact two components, the expected negative contribution due to “Joule cooling,” and an additional positive part arising from “attachment heating.” We insist that the totalentropy production be positive, in accordance with the second law, and this has the practical implication that the measurable (“bulk”) electron drift velocity must always be positive, even though the actual average (“flux”) velocity may be negative. We discuss the phenomenon physically and take as a numerical example electrons in Ar/F₂ mixtures, using Monte Carlo simulation and approximate momentum transfer theory methods to highlight the distinction between the two types of transport coefficient.The support of the Alexander von Humboldt Foundation is gratefully acknowledged. Two of the authors ~Z.P. and Z.R.! acknowledge partial support of MNTRS Project No. 1478 and collaboration and useful discussions on negative mobility with A. Napartovich, N. Dyatko, S. Sakadzˇic´, and S. Dujko.http://www.sherpa.ac.uk/romeo/issn/0021-9606..."Publishers version/PDF may be used on author's personal website, institutional website or institutional repository" from SHERPA/RoMEO site (as at 8/10/15). Copyright 2003 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in The Journal of Chemical Physics and may be found at https://doi.org/10.1063/1.1622667Keywords: Approximation theory; Computer simulation; Cooling; Electric currents; Electric field effects; Entropy; Heating; Mixtures; Monte Carlo methods; Thermodynamics; Electron drift velocity; Joule cooling; Momentum transfer theory; Negative absolute electron mo2003-12-0110.1063/1.16226672015-12-12