In the presence of an external electric field, ion transport coefficients (ion mobility and diffusion coefficients) are closely related to the ion-neutral interaction potential. A new generalized potential model, coupled to an optimized Monte Carlo technique, has been developed for the determination of the transport coefficients of polyatomic ions in weakly ionized gases. This corresponds to the polyatomic ion-molecule systems which can affect the electrical behaviour of the flue gas discharges used for the non-thermal plasma reactor for pollution control. The ion-molecule interaction has been described by a rigid core potential model which is adapted for both polar and non-polar systems and also symmetric and asymmetric systems. Momentum transfer cross sections are then determined using a semi-classical approach. The corresponding sets of cross sections including the dominant processes in our intermediate ion energy range (elastic and mainly charge transfer in certain cases) are used in the Monte Carlo code to calculate the ion transport coefficients over a wide range of reduced electric field E/N. These ion transport data fit quite well the drift tube measurements available in the literature for the CO2+/CO2 system, and also for certain weakly polar cases. The case of the H2O+/H2O system is then considered thus giving in this highly polar system the ion swarm data for the first time in the literature. Finally, we have considered with quite good reliability some asymmetric systems such as CO2+/N2 and N2+/CO2 whose ion data are also needed for flue gas discharge modelling.

The first step of this work is the determination of the elastic and inelastic ion-molecule collision cross sections for the main ions (N2+, O2+, CO2+, H2O+ and O−) usually present either in the air or flue gas discharges. The obtained cross section sets, given for ion kinetic energies not exceeding 100 eV, correspond to the interactions of each ion with its parent molecule (symmetric case) or nonparent molecule (asymmetric case). Then by using these different cross section sets, it is possible to obtain the ion swarm data for the different gas mixtures involving N2, CO2, H2O and O2 molecules whatever their relative proportions. These ion swarm data are obtained from an optimized Monte Carlo method well adapted for the ion transport in gas mixtures. This also allows us to clearly show that the classical linear approximations usually applied for the ion swarm data in mixtures such as Blanc’s law are far to be valid. Then, the ion swarm data are given in three cases of gas mixtures: a dry air (80% N2, 20% O2), a ternary gas mixture (82% N2, 12% CO2, 6% O2) and a typical flue gas (76% N2, 12% CO2, 6% O2, 6% H2O). From these reliable ion swarm data, electrical discharge modeling for a wire to plane electrode configuration has been carried out in these three mixtures at the atmospheric pressure for different applied voltages. Under the same discharge conditions, large discrepancies in the streamer formation and propagation have been observed in these three mixture cases. They are due to the deviations existing not only between the different effective electron-molecule ionization rates but also between the ion transport properties mainly because of the presence of a highly polar molecule such as H2O. This emphasizes the necessity to properly consider the ion transport in the discharge modeling.

Electron attachment processes in BF3 and BCl3 have been studied with both electron swarm and electron beam techniques. Thermal electron attachment rates were determined by the drift-dwell-drift technique to be 〈5 × 105 sec−1 · torr−1 for BF3 and 9 × 107 sec−1 · torr−1 for BCl3. Beam studies showed that F−, F2−, and BF2− were produced from BF3 by electrons of energy near 11.5 eV while Cl− and Cl2− were produced in BCl3 near 1 eV. The SF6− threshold electron impact excitation spectrum of BF3 exhibited no structure, however, a number of peaks were seen in BCl3, the chief one being near 7.6 eV. A low energy peak was observed in BCl3 at ∼ 2.5 eV. The thermal energy SF6−* ion was found to react readily with both BF3 and BCl3, yielding BF4− and BCl3F−, respectively. BF4− was also produced through the reaction F2−/BF3+BF3→ BF4−+F. Thermal energy rate constants for these reactions determined by a pulsed source method were 1.8 × 10−9, 1.6 × 10−10, and 6.1 × 10−11 cm3 molecules−1 · sec−1 in the order above.

The interaction of low energy electrons and negative ions with pure water vapor and deuterated water vapor has been studied in the following two experiments: (I) A time-of-flight electron swarm experiment has been used to determine longitudinal electron diffusion coefficients, DL, in H2O and D2O for electric-field-to-pressure ratios, E/P, from 1 to 25 V cm−1⋅Torr−1. The ratio of the longitudinal diffusion coefficient to mobility DT/μ for D2O is greater than that for H2O in the range of E/P from 5 to 20 V cm−1⋅Torr−1. Measurements of DT/μ for H2O are in agreement with the calculations of Lowke and Parker. Electron drift velocities have also been measured for values of E/P from 0.5 to 25 V cm−1⋅Torr−1, and the values for D2O are found to be considerably greater than for H2O in the range of E/P from 10 to 25 V cm−1⋅Torr−1. This result is justified on the basis of the energy dependence of the momentum transfer cross section for polar molecules. (II) Negative ions with masses in the range from 1 to 200 amu produced by electron swarm interactions and subsequent ion–molecule and ion–clustering reactions in H2O and D2O at room temperature have been recorded as a function of E/P from 0 to 70 V cm−1⋅Torr−1 and pressures from 0.1 to 5 Torr. The ions observed are H−(D−), OH− (OD−), and OH−⋅nH2O(OD−⋅nD2O) where n=1 to 7. The appearance of cluster ions from D2O occurred at a lower E/P than from H2O. This observation is compatible with our reported measurements of the characteristic electron energies (D/μ) for these vapors. The variation of the cluster ion distribution with pressure and E/P verifies the sequential clustering scheme suggested previously by Moruzzi and Phelps. For comparison purposes, negative ion products from electron swarm interactions with ammonia vapor are also presented. The ions observed are the primary ions H− and NH−2 and the cluster ions NH−2⋅nNH3 where n=1 to 4. These results are at variance with the two previous studies of ammonia.