Electron transport measurements in methane using an improved pulsed Townsend technique

An improved pulsed Townsend technique for the measurement of electron transport parameters in gases is described. The accuracy and sensitivity of the technique have been investigated by performing, respectively, electron attachment coefficient measurements in pure O₂ over a wide range of E/N at selected O₂ pressures and by determining the electron attachment and ionization coefficients and electron drift velocity in CH ₄ over a wide E/N range. Good agreement has been obtained between the present and the previously published electron attachment coefficients in O ₂ and for the drift velocity measurements in CH₄. The data on the electron attachment coefficient in CH₄ (measured for the first time) showed that with the present improved pulsed Townsend method, electron attachment coefficients up to 10 times smaller than the ionization coefficients at a given E/N value can be accurately measured. Our measurements of the electron attachment and ionization coefficients in CH₄ are in good agreement with a Boltzmann equation analysis of the electron gain and loss processes in CH₄ using published electron scattering cross sections for this molecule.