Differential cross section for H^-and NH₂^-ions in NH₃

Abstract

Differential cross section and kinetic energy distributions of H- and NH2- ions produced by dissociative attachment around 5.6 eV in ammonia have been obtained. Both H- and NH2- cross sections show a series of overlapping peaks starting at 4.94 eV with a mean spacing of 115 meV, attributed to the out-of-plane vibrational quanta n nu 2 of a NH3- resonance state. A predissociation mechanism similar to the predissociation of the lowest excited singlet state 1A2 of neutral ammonia, parent of the resonance state, and a charge transfer between two A' resonance states leading to the NH2+H- and NH2-+H products at infinite separation, in a distorted dissociation mechanism (Cs), account for the experimental observations.