Electron impact ionization cross sections of phosphorus and arsenic molecules

Abstract

This paper reports on measurements of electron impact direct ionization and dissociative ionization total cross sections of arsenic As 4 and As 2 molecules and phosphorus P 4 and P 2 molecules. Molecular species are produced by thermal effusion. The various ions resulting from electron impact are analysed by mass spectrometry. The electron energy range is 0-200 eV. For each ionization reaction, the threshold value, the behaviour in the vicinity of the threshold, as well as the main features of the curve are given. At the maximum in the ionization efficiency curve, the values of the direct ionization cross sections for P 4 , As 4 , P 2 and As 2 are respectively 17, 23.4, 7.8 and 11.4 πa 0 2 . In the same way, for dissociative ionization towards X n + where X=P and As and n=1,2 and 3, these values are in the range 1.4-3.8 πa 0 2 with an accuracy of about 16% on the values of cross sections and of 0.5 eV on those of the energy. Results are discussed against electron energy and against formation processes Mesures des sections (efficaces totales d'ionisation simple ou dissociative sous impact d'electrons (0-200 eV) de As 4 , As 2 , P 4 , P 2 (obtenues par effusion thermique) avec, analyse des ions formes par spectrometrie de masse. Discussion des resultats en fonction de l'energie des electrons et des processus de formation