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

Abstract

Electron impact ionization of carbon dioxide has been studied as a function of electron energy up to 180 eV with a double focussing mass spectrometer. Absolute partial ionization cross section functions have been measured for the processes CO₂+e→CO₂⁺+2e and CO₂+e→CO₂⁺⁺+3e by normalization against the Ar⁺ ionization cross section. Using nth root extrapolation, the following minimum ionization potentials have been derived from the low energy cross section function: CO₂⁺(X ²Π_g) =13.79±0.05 eV and I.P.(CO₂⁺⁺) =37.2±0.5 eV. For the doubly ionized parent molecule, a square law dependence of the cross section has been found from threshold up to some 10 eV above onset. All results obtained are compared with previous determinations where available.