Electron mobilities in low density hydrogen and carbon monoxide gases: Momentum transfer cross sections at very low energies

Values of the momentum transfer cross sections σm of hydrogen and carbon monoxide molecules for very low energy electrons (1--300 meV, 0.2--50 zJ; z=zepto=10-21 ) have been refined by electron mobility measurements in the gases over wide ranges of temperature. This is part of an ongoing study of effects of molecular shape on electron transport in fluids. Electron mobilities in hydrogen gas at temperatures 17--450 K are roughly consistent with previously reported values of σm, but do not exclude the possibility of a σm minimum of 5.2x10-20 m2 at an electron energy ξ≤0.7 zJ. Carbon monoxide molecules have a minimum σm of 5.8x10-20 m2 at ξ=5 zJ. A new treatment of low energy electron scattering by CO is needed