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

Differential cross section and kinetic energy distributions of N(-) 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 of a NH3(-) resonance state. A predissociation mechanism similar to the predissociation of the lowest excited singlet state A-prime of neutral ammonia, parent of the resonance state, and a charge transfer between two A-prime 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.