Zero-field mobility of excess electrons in dense methane gas

Measurements of the low-field mobility of electrons are reported for dense methane gas above the critical temperature. Use of a thick-walled stainless steel cell permitted measurements to 200 atm or a density of 0.3 g/cc at -77°C. At low densities the mobility follows a (density)−1 dependence and increases with increasing temperature. The mobility goes through a maximum of about 1000 cm2/V sec at a density of 1×1022 molecules/cc. The variation in mobility at high densities depends primarily on fluid density and less on either fluid structure or temperature. The position of the mobility maximum is expected to correlate with a minimum in the energy of the lowest electronic eigenstate.