Double Rydberg anions with solvated ammonium kernels: Electron binding energies and Dyson orbitals
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 a(1) 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.