Electron drift velocities, w, as a function of temperature were measured and on the basis of these data, Ramsauer-Townsend (RT) minima were found in the cross section for momentum transfer, sigma m, for all these gases. The position of the RT minimum and the magnitude of the corresponding sigma m at the energy where the minimum occurs are 0.12, 0.14, 0.14, and 0.25 eV and 1.2, 3.0, 4.6, and 5.8*10-16 cm2 for ethane, propane, butane, and neopentane, respectively. The density dependence of the w for neopentane was also investigated. This latter investigation and similar ones in the literature on methane, ethane, and propane are discussed in connection with the observed RT minima and the mobility of thermal electrons in the low- and high-pressure vapours and the liquids of these compounds.
A molecular dynamics study of electronic absorption line broadening in highpressure nonpolar gases Drift velocities w for slow electrons in NH J vapor have been measured and are reported as a function of the density-reduced electric field E/N (::;24XlO-17 V cm'), density N (2.43-292 X 10 18 moiecuiecm-3 ), and temperature T (300-650 K). The w decreases with increasing N considerably and this decrease varies with T· for a fixed N it is higher the lower the T. Use is made of the Tand N -dependence of w to assess the role of the various processes which delay the electron drift. The density range above _2.5x10 19 molecules cm-J seems to represent the transition from the free (or quasifree) to the localized (anionic) electron state. The number density NL at which complete electron localization occurs, has been estimated at various T. At T = 300 K, NL ",,3.3 X 10'0 molecule cm-J or -0.01 g cm J • Estimates have also been made of the binding energy of the electron to the trapping species (possibly NH J clusters) which, depending on T, range from 0.11 toO.15 eV.
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