Electron mobility maximum in dense argon gas at low temperature

Abstract

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 (T c = 150.7 K), as a function of the gas density N up to 14 atoms·nm −3 (N c = 8.08 atoms·nm −3 ). For the first time a maximum of the zero-field density-normalized mobility µ 0 N has been observed at the same density where it was detected in liquid Argon under saturated vapor pressure conditions. The existence of the µ 0 N maximum in the liquid is commonly attributed to electrons scattering off longwavelength collective modes of the fluid, while for the low-density gas a densitymodified kinetic model is valid. The presence of the µ 0 N maximum also in the gas phase raises therefore the question whether the single scattering picture valid in the gas is valid even at liquid densities.

Scattering Properties of Argon Gas in the Temperature Range 87.3-120 K

“…(5), one concludes that this term is indeed negligible. The minimum is evidence for the atomic RamsauerTownsend effect [30], occurring in the collision between two bodies when the total cross-section is a minimum and, therefore, the mobility is a maximum [31]. This minimum arises from a delicate balance between the attractive long-range and repulsive short-range interactions.…”

Electron and ion transport in dense rare gases

“…In this way, the temperature T is not density N for He (squares) [9], Ne (triangles) [10], Ar (closed dots) [11,12], Xe (open dots) [13]. The constant lines are the prediction of kinetic theory.…”

Electron mobility in dense Argon gas at several temperatures

“…It has been therefore suggested that the use of the WS model at such high densities might not be appropriate anymore [12,13,16].…”

“…(1). Anomalous density effects have been experimentally observed in a number of compressed gases [2][3][4][5][6][7][8][9][10][11][12][13]. A negative density effect, i.e., the density-normalized mobility at thermal energies, 0 N, decreases with incresing N at constant T (and eventually drops rapidly to very low values because of the formation of localized electron states), is shown by gases, such as He and Ne, whose interaction with the excess electrons is dominated by the short-range repulsive exchange forces.…”

“…However, the results and the analysis of accurate measurements in Ne [10,11] and in Ar [12,13] (but also in liquid Ar [16]), two gases, whose momentum transfer scattering cross sections, though for different physical reasons, depend strongly on the electron energy, have shown that the different behavior of the mobility in repulsive and attractive gases can be rationalized in an unified picture, if all multiple scattering effects are taken into account heuristically.…”