$OH3−$ and $O2H5−$ double Rydberg anions: Predictions and comparisons with $NH4−$ and $N2H7−$

A low barrier in the reaction pathway between the double Rydberg isomer of $OH3−$ and a hydride-water complex indicates that the former species is more difficult to isolate and characterize through anion photoelectron spectroscopy than the well known double Rydberg anion (DRA), tetrahedral $NH4−$⁠. Electron propagator calculations of vertical electron detachment energies (VEDEs) and isosurface plots of the electron localization function disclose that the transition state’s electronic structure more closely resembles that of the DRA than that of the hydride-water complex. Possible stabilization of the $OH3−$ DRA through hydrogen bonding or ion-dipole interactions is examined through calculations on $O2H5−$ species. Three $O2H5−$ minima with $H−(H2O)2$⁠, hydrogen-bridged, and DRA-molecule structures resemble previously discovered $N2H7−$ species and have well separated VEDEs that may be observable in anion photoelectron spectra.