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

Abstract

Electron impact ionization has been studied in NH3 and in a mixture of NH3 and ND3 as a function of electron energy up to 180 eV with a double focusing mass spectrometer. Absolute partial ionization cross section functions have been obtained in NH3 for the production of NH+ 3, NH+ 2, NH+, N+, H+ 2, H+, and NH++ 3 by normalization against the Ar ionization cross section. The ions NH++ 2 and N++, produced by the process NH3+e, have been found for the first time, and an estimate of the ionization cross section is given. From the measured partial ionization cross section functions the total ionization cross section function of NH3 has been deduced. In addition, it has been possible to measure the ratio of the partial cross section for double and single ionization of the parent ions ND2H and ND3 as a function of electron energy. The ionization cross section results obtained are compared with previous determinations where available and with a recent semiempirical total ionization cross section calculation by Jain and Khare. Using nth root extrapolation the following ionization and appearance potentials have been derived fom the low energy cross section function: I.P. (NH+ 3/NH3) =10.4±0.1 eV; A.P. (NH+ 2/NH3) =16.5±0.2 eV; A.P. (NH+/NH3) =22.9±0.5 and 27.2±0.5 eV; A.P. (N+/NH3) =29.5±0.5 eV; A.P. (H+ 2/NH3) =14.8±0.2 eV; A.P. (H+/NH3) =23.0±0.2, 27.7±0.5, and 30.6±0.5 eV; I.P. (ND2H+/ND2H) =10.5±0.1 eV; I.P. (ND+ 3/ND3) =10.7±0.1 eV; I.P. (NH++ 3/NH3) =34.4±0.2 eV; I.P. (NDH++ 2/NDH2) = 34.6±1.0 eV; I.P. (ND2H++/ND2H) =34.6±0.5 eV; and I.P. (ND++ 3/ND3) =34.6±0.5 eV. For the doubly ionized parent molecules a square law has been found from threshold up to some 20 eV above onset. The ionization and appearance potentials obtained are also compared with such earlier results as are available.