Three-body attachment in oxygen and an air-like nitrogen and oxygen mixture

Calculations of the three-body attachment coefficient eta3/N, N being the gas number density, in oxygen and an air-like nitrogen and oxygen mixture, are performed using a Boltzmann equation method. First, an appropriate cross-section Qa3for this attachment process in oxygen is deduced by modifying that of Spence and Schulz (1972) so that the calculated eta3/N agrees well with the experimental values of Grunberg (1969). Then, the deduced Qa3is used for the calculation of eta3/N in an air-like mixture of 79% nitrogen and 21% oxygen. Good agreement is obtained with the eta3/N values measured for dry air by Hessenauer (1967) at low E/N, where E is the electric field. The variation of eta3/N2with N is studied, and it is found that even though the value of Qa3is assumed to be proportional to N, eta3/N2can decrease with increasing N due to the change in the electron energy distribution, caused by the variation of Qa3.