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.