Photodetachment spectroscopy of cluster anions. Photoelectron spectroscopy of H–(NH3)1, H–(NH3)2 and the tetrahedral isomer of NH –4

Abstract

The dominant peaks in the photoelectron spectra of the gas-phase, negative cluster ions H^–(NH₃)₁ and H^–(NH₃)₂ provide evidence for describing them as ion-molecule complexes comprised of intact hydride ions which are solvated by ammonia. Vertical detachment energies ad approximate ion–single-solvent dissociation energies are obtained. Other spectral features reveal the complexation-induced distrotion of the ammonia solvent(s) by their hydride sub-ions. In the photoelectron spectra of H^–(NH₃)₁ and additional peak appears which is small and unusually narrow and which does not shift upon deuteration. Evidence is presented for interpreting this peak as arising due to the photodetachment of a tetrahedral isomer of NH^–₄. This previously unknown ammonium anion is not a cluster species, and it is described as a NH⁺₄ ion core with two Rydberg-like electrons.