Measurement of Ionization and Attachment Coefficients in Carbon Monoxide in Uniform Fields

Measurements of pre-breakdown currents in uniform field conditions, in carbon monoxide at different pressures, in the E/p range of 36 to 200 v cm -1 (mm Hg) -1 indicate the presence of electron attachment. It is suggested that the mechanism of negative ion formation is due to dissociative attachment, therefore values of α and the dimensionally equivalent attachment coefficient η have been computed from the semi-logarithmic plots of current against electrode separation, by employing the modified Townsend equation for the growth of current. Static breakdown potentials have been measured up to pd~ 1050 mm Hg cm (where p is the pressure and d the gap length) and show that Paschen's law is obeyed. Further, the values of secondary coefficient γ have been computed from upcurving of the semi-logarithmic plots of current against electrode separation. The values of breakdown potential calculated from the breakdown criterion are in good agreement with the measured values, showing that the static breakdown in carbon monoxide is brought about by the Townsend build-up mechanism. The mean cross sections for ionization and attachment have been calculated for various electron mean energies from the mean values of α/p and η/p obtained from the present study and compared with the values computed from low pressure single collision data, by assuming either a Maxwellian or a Druyvesteyn distribution of electron energies. It is concluded that the Maxwellian distribution is satisfactory to explain the results but the Druyvesteyn distribution does not seem to apply. Calculations show that the electron attachment observed in this study is due to resonant attachment processes occurring at about 10 ev and the contributions due to processes of a continuous nature at about 21 and 23 ev are negligible.