Ionization and attachment coefficients in CO2 : N2 : He and pure CO2

Values of the ionization (α/N) and attachment (η/N) coefficients have been determined from spatial current growth measurements in uniform fields E for a CO2 : N2 : He (1 : 2 : 3) mixture and for pure CO2 over the ranges 4.66×10−16⩽E/N⩽8.48×10−16 V cm2 and 7.63×10−16⩽E/N⩽9.89×10−16 V cm2, respectively, where N is the gas density. The limiting values of E/N, at which α=η, are found to be (4.66±0.14) ×10−16 V cm2 and (8.20±0.16) ×10−16 V cm2 for the CO2 : N2 : He mixture and for CO2, respectively. The present values of the coefficients are in reasonably good agreement with those calculated from a solution of the Boltzmann equation using electron-collision cross sections. Nevertheless, the present results indicate that even closer agreement would be obtained if the attachment cross section used in the calculations is reduced by about 15%.