Distorted spectra were obtained when the Mn K x‐ray peak was observed in a proportional counter filled with CO2and small pressures of the counter poison O2. The spectra can be explained with the assumption that the only effect of the poison is to capture electrons as they drift toward the anode. The rate of attachment of electrons at an average electron energy of 0.054 eV and 298°K was found to be equal toK2(O2)+K3(O2)(CO2), where the values ofK2andK3are 5×10−12cc/sec and 1.7×10−30cc2/sec, respectively.