Measurement of the attachment of thermal electrons to oxygen molecules in the proportional counter with mixture CO2 + O2

Measurements were undertaken at the pressure range from 400 to 1900 Tr of CO2 and from 10 to 50 m Tr of O2. The gas was ionized by 5.9 keV X-rays from a Fe-55 source. The results of measurements can be described by the term ν'3 of the three-body attachment processes, i.e. - (1/n).(dn/dt)=ν'3[CO2] [O2], where: n - number of the electrons, t - time, [CO2] and [O2] - density of the respective molecules. The coefficient ν'3 is a function of the mean amplitude value U of the pulse spectrum without oxygen according to the relation ν'3=ν'30/(1 + γU). ν'30=(3.18 +- 0.15).10-30 cm6/s, is in good agreement with other results given by means of the drift tube technique, γ-0.089 mV-1. A short discussion of the possible physical processes that might affect ν'3 is given. (author)