Cross-sections for the electron impact ionization of ND x ( x =1−3)

Abstract

Absolute cross-sections for the electron impact ionization and dissociative ionization of the ND 3 molecule and the ND 2 and ND free radicals were measured from threshold to 200 eV using the fast neutral beam technique. The deuterated rather than protonated targets were used in this work to facilitate a better separation of the various product ions from a given parent in our apparatus. A common feature of all three targets studied in this work is a dominant parent ionization cross-section with absolute values (at 70 eV) of 1.21 × 10 −16 cm 2 (ND 3 +), 1.44 × 10 −16 cm 2 (ND 2 +) and 1.45 × 10 −16 cm 2 (ND +). Dissociative ionization processes for all three targets are less significant, with a single dissociative process dominating in each case, the removal of a single D atom (ND x + e − → ND x−l + + D + 2e −). The cross-section for this dominant dissociative ionization channel decreases from 1.03 × 10 −16 cm 2 for ND 2 + ND 3 to 0.85 × 10 −16 cm 2 for ND + ND 2 to 0.40 × 10 −16 cm 2 for N + ND . The measured appearance energies for the various fragment ions indicate that all fragment ions, except for D +, are formed with little excess kinetic energy. Our experimental data for ND 3 are compared with existing experimental and theoretical data for NH 3.