The gravity effect and the mobility of electrons in critical neopentane

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Abstract
The rapid change of density with temperature, the high compressibility of the vapor and liquid near the critical region, and the force of gravity make it difficult to avoid a density gradient in the ’’critical fluid’’. Electron mobilities were measured simultaneously in the juxtaposed vapor and liquid so that density changes could be monitored. The mobility in neopentane at the critical density and ∼0.1 K above Tc is 45 cm2/V s; the estimated mobility in the critical fluid is 42 cm2/V s. The effect of electric field strength on the mobility changes sign at the reduced density and temperature n/nc=1.2 and T/Tc=0.995. The reversal is attributed to the Ramsauer–Townsend scattering minimum occurring at an energy slightly above thermal at this density.