Dissociative Attachment of Electrons in Ammonia and Ammonia-d3

Abstract

Cross sections for total negative ions and amino negative ions have been measured as a function of energy for dissociative attachment of electrons in the gases NH₃ and ND₃. Two peaks are observed, at 5.65 and 10.5 eV. Both peaks contain H⁻(D⁻) and NH₂⁻). Small direct isotope effects were found, in negative ion production, except for H⁻/D⁻ formation at 5.65 eV where the isotope effect was 1.0. The peak at 5.65 eV leads to products in their ground states. The corresponding potential‐energy‐vs‐internuclear‐distance (H–NH₂) curve for NH₃⁻ may contain a hump or may merely have a shallow slope in the Franck–Condon region. The peak at 10.5 eV arises from a repulsive state of NH₃⁻, and the amino fragment is formed in an excited state. Empirical trends in the isoelectronic series methane, ammonia, and water are identified.