Ionization of phosphine and deuterated phosphine by electron impact from threshold up to 180 eV

Abstract

Electron impact ionization has been studied in PH3 and in a mixture of PH3 and PD3 as a function of electron energy up to 180 eV, with a double focusing mass spectrometer. Absolute partial ionization cross sections have been obtained in PH3 for the production of the parent ion PH+3, for the fragment ions PH+2, PH+, P+, H+2, and H+ and for the doubly charged ions PH++3, PH++2, PH++, and P++ by normalization against the Ar ionization cross section. From the measured partial ionization cross sections the total ionization cross section function of PH3 has been deduced. In addition, it has been possible to obtain the cross section ratios q (PD++3)/q (PD+3), q (PD++2)/q (PD+3), q (PD++)/q (PD+3), and q (P++)/q (PD+3) as a function of electron energy. The ion D++3, produced by the process PD3+e, has been found for the first time and an estimate of the ionization cross section is given. Using nth root extrapolation the following ionization and appearance potentials have been derived from the low energy cross section functions: I.P. (PH+3) =10.1±0.1 and 12.5±0.2 eV; I.P. (PD+3) =10.15±0.1 and 12.75±0.2 eV; A.P. (PH+2) =14.2±0.2 eV; A.P. (PD+2) =14.3±0.2 eV; A.P. (PH+) =13.0±0.2 eV; A.P. (PD+) =13.3±0.2 eV; A.P. (P+) from PH3=17.2±0.3, 18.8±0.3, and 23.5±0.3 eV; A.P. (P+) from PD3=17.7±0.3, 19.5±0.3, and 22.0±0.3 eV; A.P. (H+2) =14.8±0.2 and 24.8±0.5 eV; A.P. (D+2) =14.9±0.2 and 24.8±0.5 eV; A.P. (H+) =25.3±0.5 eV; A.P. (D+) =25.3±0.5 eV; I.P. (PH++3) =30.0±1.0 eV; I.P. (PD++3) =29.8±0.5 eV; A.P. (PH++2) =35.0±0.5 eV; A.P. (PD++2) =34.9±0.5 eV; A.P. (PH++) =33.0±1.0 eV; A.P. (PD++) =34.4±0.5 eV; A.P. (P++) from PH3=45.6±0.5 eV; and A.P. (P++) from PD3=46.7±0.5 eV. In all double ionization cases a square law has been found from threshold up to some 5–10 eV above threshold. The ionization and appearance potentials obtained are compared with previous results where available. It is possible to resolve a yet unexplained discrepancy of the ionization potentials of the doubly ionized ions of PH3.