Density and temperature effects on electron mobility in gaseous, critical, and liquid ethene

Contrary to previous reports, the electron scattering cross section of ethene molecules has a Ramsauer-Townsend (RT) minimum at 0.09-0.10 eV. The energy of the RT minimum is much higher than that for nitrogen, slightly lower than that for ethane, and much lower than those for methane and xenon. The scattering of low-energy (${10}^{-3\mathrm{}}$-1 eV) electrons by nonpolar molecules in the low-density gas phase is strongly influenced by the molecular shape. The mobility of electrons (the proportionate rate of motion in the direction of an applied electric field) in the low-density gas is mainly governed by elastic collisions, but the removal of energy gained from the field occurs mainly through inelastic collisions. The latter must involve predominantly molecular rotational transitions at the energies involved (<0.1 eV). In the dense gas at $\frac{n}{n_c}\gtrsim 0.2$ the density-normalized mobility $\mu n$ decreases due to electron quasilocalization and transient-anion formation. The transient anions in ethene are much more ephemeral than those formed in dense nitrogen vapor. The anion state becomes less ephemeral with increasing density and decreasing temperature in the liquid phase.