Electron-impact ionization of NH3 and ND3

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 irrespecti ve of their initial kinetic energies. Data are presented for the production of (NH3+ + NH2+ + NH+ + N+), H+, H-2(+), and NH32+ from NH3 and for produc tion of ND3+, ND2+, ND+, N+, D+, D-2(+), and ND32+ from ND3 and for the tot al cross sections which are obtained as the sum of these partial cross sect ions. Data are also presented for formation of (ND+,D+) and (N+,D+) ion pai rs. 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 n o discernible effect upon the cross sections and that the partial cross sec tions for many of the lighter ions are much larger than had been previously reported. (C) 2001 American Institute of Physics.