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Values of the ratio of the longitudinal diffusion coefficient to mobility DL/μ for electrons in He, Ar, Kr, and Xe are derived from current waveforms obtained during earlier measurements of electron mobility. The electric field to gas density ratios E/N cover the wide range of 10−3 to 20 Td, thereby bridging previous experiments at low E/N to recent experiments at high E/N. Here 1 Td=1×10−21 V m2. The corresponding DL/μ values range from 0.0066 eV for thermal electrons at 77 K to 10 eV. In addition to the well-known peak in DL/μ for Ar at E/N between 0.01 and 0.1 Td caused by the Ramsauer minimum in the momentum transfer cross section, we find previously unreported low-energy peaks in DL/μ vs E/N in Kr and Xe and previously unreported pronounced leveling-off in DL/μ at E/N≳8 Td in Ar, Kr, and Xe. Calculations of transport coefficients using numerical solutions of the Boltzmann equation and cross section sets in the literature give good agreement with experiment from E/N producing thermal electrons up to average energies ≊10 eV and E/N up to 100 Td, the upper limit of our calculations. The leveling off of DL/μ at high E/N is caused by inelastic collisions.

Electron attachment and detachment coefficients are reported for pure oxygen from analyses of the current waveforms observed in drift-tube experiments. The results are consistent with the identification of the negative ion as O2− with an electron affinity of 0.43±0.02 eV. The two-body collisional detachment coefficient for O2− in thermal equilibrium with the gas increases from 9×10−17 cm3/sec at 375°K to 1.4×10−14 cm3/sec at 575°K. The three-body attachment coefficient for thermal electrons increases from 2.0±0.2×10−30 cm6/sec at 300°K to 2.8±0.5×10−30 cm6/sec at 530°K. The O2− ions are found to survive at least 3×108 elastic collisions without de-excitation and so are believed to be in their lowest vibrational state. At low oxygen densities the current of detached electrons is separated from the negative-ion current by applying a high-frequency voltage to the control grid. At high oxygen densities the electrons and negative ions cross the tube in a narrow pulse at a drift velocity determined by the equilibrium concentrations of electrons and ions.

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Electron-attachment coefficients in O2–CO2 and O2–H2O mixtures and electron-attachment—detachment equilibrium constants for O2–CO2 mixtures are obtained from drift-tube measurements similar to those used previously for O2. The three-body attachment coefficients involving O2 and CO2 are 3.1×10−30, 4.0×10−30, and 2.7×10−30 cm6/sec at 300°, 477°, and 525°K. The electron—negative-ion equilibrium constant data correspond to the formation of a CO4− with a large degree of freedom of internal motion and with an energy of dissociation into O2− and CO2 of 0.8 eV. The three-body attachment coefficient involving O2 and H2O is 1.4±0.2×10−29 cm6/sec at 300° and 395°K. In O2–H2O mixtures at temperatures of 500° and 555°K we observe the conversion of O2− to a more stable negative-ion form which shows no evidence of dissociation or detachment.