Double Rydberg anions with solvated ammonium kernels: Electron binding energies and Dyson orbitals

Abstract

Ab initio electron-propagator calculations on the electron detachment energies and associated Dyson orbitals of NnH3n+1− for n = 1–5 confirm the assignment of low-energy peaks in anion photoelectron spectra to double Rydberg anions, species in which a closed-shell cation binds a diffuse pair of electrons. The most stable double Rydberg anions contain NnH3n+1+ cores, wherein the NH4+ kernel forms n − 1 hydrogen bonds with ammonia molecules. Other low-energy peaks for a given n pertain to double Rydberg anions of lower n that are weakly bound to ammonia molecules. High-energy peaks arise from the most stable isomers which consist of hydrides bound to N–H bonds of coordinating ammonia molecules. Dyson orbitals of electron detachment are distributed over the periphery of the bonding regions of the NnH3n+1+ cores. For n = 2–4, negative charge accumulates mostly outside the N–H bonds of the NH4+ kernels that are not engaged in hydrogen bonds. For the tetrahedral cases, where n = 1, 5, Dyson orbitals are diffuse, symmetric functions that are orthogonalized to occupied a1 orbitals of the cationic core. Shake-up features in spectra have been assigned to doublet states with a single diffuse electron in an s, p, d, or f orbital.