Effect of molecular solutes on the electron drift velocity in liquid Ar, Kr, and Xe

Measurements of the electron drift velocity in liquid argon, krypton, and xenon were performed in an electric field up to 100 kV cm^-1. At higher field strengths saturation velocities were observed in agreement with other authors. The addition of a small concentration of molecular solutes leads to an increase of the electron drift velocity above the saturation value of the pure liquid. The drift velocity either reaches a higher constant value or passes through a maximum at field strengths greater than 10⁴ V cm^-1. This effect was investigated as a function of solute concentration for N₂, H₂, methane, ethane, propane, and butane. Inelastic energy losses in collisions of electrons and solute molecules are assumed and by means of the Cohen-Lekner theory the energy dependence of the loss processes is derived.