Cross section for single and double ionization of carbon monoxide by electron impact from threshold up to 180 eV

Electron impact ionization of carbon monoxide has been studied as a function of electron energy up to 180 eV with a double focusing mass spectrometer Varian MAT CH5. Absolute partial ionization cross section functions have been obtained for the processes CO +e→CO++2e and CO+e→CO+++3e by normalization against the Ar+ cross section with help of the method of molecular effusive flow. In the case of CO++ the results suggest, in accordance with previous authors, that this ion exists in a metastable state with a mean half-life in the range of 6–15 μs. Using nth root extrapolation, the following minimum ionization potentials have been derived from the low energy cross section function: CO+(X 2Σ+) = (14.07±0.05) eV and CO++= (41.8±0.5) eV. All experimental results presented are compared with previous determinations where available.