Electron mobility maximum in dense argon gas at low temperature

We report measurements of excess electron mobility in dense argon gas at the two temperatures T=152.15 and 162.30 K, fairly close to the critical one (Tc=150.7 K), as a function of the gas density N up to 14 atoms nm−3 (Nc=8.08 atoms nm−3). For the first time a maximum of the zero-field density-normalized mobility μ0N has been observed at the same density where it was detected in liquid argon under saturated vapor pressure conditions. The existence of the μ0N maximum in the liquid is commonly attributed to electrons scattering off long-wavelength collective modes of the fluid, while for the low-density gas a density-modified kinetic model is valid. The presence of the μ0N maximum also in the gas phase raises therefore the question as to whether the single scattering picture valid in the gas is valid even at liquid densities.