Electron mobility in dense Argon gas at several temperatures

We report measurements of electron mobility /spl mu/ in Ar gas in a range below and above the critical point. /spl mu/ is measured as a function of the electric field E for densities up to N < 100 /spl times/ 10/sup 26/ m/sup -3/, encompassing the critical density (N/sub c/ = 80.8 /spl times/ 10/sup 21/ m/sup -3/), for T=142.8, 152.2, 177.3, and 199.7 K The data confirm the model proposed for the positive density effect observed in the zero-field density-normalized mobility /spl mu//sub 0/N in Argon at T=162.7 K We observe that below the critical temperature T/sub c/ = 150.9 K the density effect is neither positive nor negative. This is consistent with the observation that at 90 K /spl mu//sub 0/N shows a negative effect in contrast with its behavior at room temperature. The modified kinetic-theory model accurately describes the T, N, and E dependence of /spl mu/N mainly by including a density dependent shift of the ground state energy of the electrons that affects the cross section.