Single and double ionization of nitrogen dioxide by electron impact from threshold up to 180 eV

Abstract

Electron impact ionization of nitrogen dioxide has been studied as a function of electron energy up to 180 eV with a double focussing mass spectrometer Varian MAT CH5 and an improved Nier type electron impact ion source. We report the first observation of NO₂⁺⁺ produced via electron impact. Relative partial ionization cross section functions have been obtained for the processes NO₂+e→NO₂⁺+2e and NO₂+e→NO₂⁺⁺+3e. An accurate measurement of the cross section ratio q (NO₂⁺⁺/NO₂) /q(NO₂⁺/NO₂) has been performed. In addition an estimate of the absolute partial cross sections has been made normalizing the measured relative cross section against the Ar⁺ cross section with the method of molecular effusive flow. Using the nth root extrapolation the following ionization potentials have been derived from the cross section functions near threshold: NO₂⁺ = (10,4±0,3) eV and NO₂⁺⁺ = (35,0±0,5) eV.