Electron-impact ionization of NH₃ and ND₃

R. Rejoub, B. G. Lindsay, and R. F. Stebbings

J. Chem. Phys. 115, 5053-5058 (2001)

Absolute partial and total cross sections for electron-impact ionization of NH₃ and ND₃ are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for the production of (NH₃⁺ + NH₂⁺ + NH⁺ + N⁺), H⁺, H₂⁺, and NH₃²⁺ from NH₃ and for production of ND₃⁺, ND₂⁺, ND⁺, N⁺, D⁺, D₂⁺, and ND₃²⁺ from ND₃ and for the total cross sections which are obtained as the sum of these partial cross sections. Data are also presented for formation of (ND⁺, D⁺) and (N⁺, D⁺) ion pairs. The overall uncertainty in the absolute cross sections for most of the singly-charged ions is ±6-8% while that for doubly charged ions is ±20%. It is observed that the isotopic composition of the ammonia target has no discernable effect upon the cross sections and that the partial cross sections for many of the lighter ions are much larger than had been previously reported.