Structures and properties of double-Rydberg anions

Abstract

Double-Rydberg anions consist of a closed-shell cation core and two Rydberg-like, diffuse electrons. Ground-state geometry optimizations disclose stable minima for OH{sub 3}{sup {minus}}, NH{sub 4}{sup {minus}}, and PH{sub 4}{sup {minus}} but not for SH{sub 3}{sup {minus}}, FH{sub 2}{sup {minus}}, and ClH{sub 2}{sup {minus}}. An alternative PH{sub 4}{sup {minus}} structure with C{sub 2v} symmetry, based on valence shell electron pair repulsion theory, is a more stable minimum than its double-Rydberg counterpart. Vibrational frequencies of the minima are reported. Other optimizations of alternative structures based on valence shell electron pair repulsion theory converge either to double-Rydberg minima or to transition states. Electron propagator calculations yield ionization energies for the minima.