Swarm Determination of the Cross Section for Momentum Transfer in Ethylene and in Ethylene Mixtures

Abstract

Data are reported on the temperature dependence of electron‐swarm drift velocities w in ethylene. The analysis of the data gave a velocity‐independent cross section for momentum transfer, σ_E for ethylene at thermal electron energies. Using a constant σ_E, we investigated the dependence of w_E/w_M on gas concentration, where w_E is the drift velocity in ethylene and w_M that in mixtures of ethylene with a polar impurity P. Three regions of concentration were distinguished: initial, intermediate, and final. The initial region can provide information about the velocity dependence of σ_P, the intermediate (better suited for experimentation) can easily provide σ_P if the velocity dependence of σ_P is known, and the final region provides a new way to measure the drift velocity for pure polar compounds P by simply measuring w_E/w_M in mixtures of P with ethylene. The latter is extremely important when P cannot be studied alone.